I have to assume it's from commuting-I never used to have a problem before I started.

I'm getting plenty of sleep at nights, I'm eating better than I was before I started riding so much, but I just get soooo sleepy in the afternoons. Not just, 'oh, i feel a little tired', but 'i want to sneak home and get into bed for 3-4 hrs'. My ride in the morning is only 3 miles, and i've been doing it for about 2 weeks now. I've been riding frequently (avg. 10 miles a day) for about a month. what can I do to shake the sleepies? I don't want to go back to driving a car, but I'm terribly unproductive in the afternoons now.

Give it two more weeks! :-) It is a natural reaction, and much like dieting, your body needs to adjust to the new treatment you are giving it.

sometimes i need some afternoon caffine.

Why not take a short nap? I'm putting in practically the same miles and I too have succumb to this afternoon slump. It doesn't happen every day but when it hits, I just go ahead and nap (usually 30 minutes to an hour). When I wake up, I usually find that I'm ready to get back out on the bike. If you don't have time for a nap, then... well I don't know. Just take a nap.

How much sleep are you actually getting? What was plenty before you started riding a lot may not be enough, given your now-higher amount of physical activity. Especially if you went from no activity to riding ten miles a day. The bigger your increase in activity, the more recovery (sleep) time you'll require until you get adjusted.

After a while though, you should start getting used to the extra activity and having more energy. I've been running and cycling regularly for about three years now, and never really noticed how much more energy I had until I lost it due to injury. I started training for a marathon, I got overzealous with my runs and gave myself shin splints. I ignored them for a while and they got really, really bad. So bad that I had to stop running and cycling because just walking became extremely painful. I was unable to exercise for about a month, and by the end of the month, I started to feel really lethargic. When I started running again, I felt sleepy afterwards for a week or two.

Hang in there, it'll work itself out.

If you eat too many simple carbohydrates at lunch time, you may experience this. You might want to try switching your lunch to more salads, fresh vegetables, proteins, and fats with less bread, potatoes, sugar, etc.

It's funny that I am reading this right as I start to perform my "after lunch and pre commute home ritual".
This used to happen to me all the time, I'd get so sleepy I'd get cold and sweaty and feel weak as hell. Now, about half way between lunch and my 14 mile commute home I eat one or two peanut butter and jelly sammiches and drink a glass of fruit juice. The carbs in the jelly and fruit juice give me a boost of energy immediately and the protien in the peanut butter keeps me going in the long run. I still cary a snickers bar or a quaker oatmeal "trail mix" bar in my panier in case I feel a need for a refuel on my way.
Now I have a routine for my commute.
Morning before the commute - quaker trail mix bar and glass of OJ
Breakfast at work - Oatmeal and whole weat toast and coffee
Lunch at work - Usually one or two PB&J sammiches on whole wheat and water
Afternoon pre-commute - Same as lunch and a glass of juice

Haven't had the problem ever since

I'm getting roughly 8 hours of sleep. I have no problem getting to bed early, but I don't think I can sleep more than 8 hrs. I'll just wake up earlier.

I'm pretty aware of what I'm eating, so I don't think it's the carb rush, or the 'all the blood is digesting the huge lunch' scenario either. I usually have a banana before leaving the house, some nuts, or a clif bar mid morning, and a small sandwich for lunch. And I'm sleepy despite enough caffeine to kill a small elephant.

Perhaps it is that by body isn't used to the extra exertion. I'll give it time, and hope my body adjusts. If I could take a nap, I would, but if I was caught snoozing, i'd get fired...

You get lunch, don't you? Take a quick cat nap then. I set my watch to alarm at around 1300 and go back to work. It actually makes me more alert during the afternoon. Especially when I have to go hear a lecture on "The thermodynamics of biomass conversions utilizing oxygen deprived nitrogen rich atmospheres as applied to thermochemical processing of wood and plant fiber." Mainlining pure caffeine can hardly keep you awake during that.

DING! DING! DING! ...excellent advice...ditto.

And thus, America re-discovers what many of our Presidents and more Euros swear by, the early afternoon siesta!

Power napping.

Make sure you are hydrated. Sleepiness is also a sign of dehydration.

I got the same thing in the first month of commuting whe I first started... Then it slowly went away.

Have you increased your caffeine to try to compensate? I'm a big caffeine addict, but there's a point, especially late afternoon or early evening, where a big ole coffee knocks me out tired. Go figure.

Maybe you need to ride more. I usually ride at least 15 miles/day, and I have way more energy all the time than when I started. I don't even use an alarm to wake up anymore. Maybe it varies per person, but since I started cycling, I feel awake and alert when I wake up, and feel energetic and focussed throughout the day. I go to bed at the same time every night +/- 30 minutes and rarely have any trouble falling asleep.

The exception to this is if I ride within an hour or two of bedtime.

Edit: When I started cycling, I cut soda out of my diet, which accounted for 95% of my caffiene intake too.

Nah, I've always been a big coffee drinker- to the point, that I doubt it has much of an impact at all anymore. I can have a cup at 8PM, and be asleep by 10.

Regarding the diet, I don't eat a lot of simple carbs- I don't avoid them completely, but I try to balance with some protein, fibrous carbs, etc.

I'll stick it out, and see what happens after a few more weeks of this.

Thought I'd update a bit- I didn't ride at all yesterday (didn't drive either- worked from home), and even though I was still tired, I think my body appreciated the rest. The commute in this morning was easy, I felt very strong, and didn't get a bit tired throughout the day today. And I'm looking forward to an aggressive ride home. So sleep wasn't the fix, but rest was... I think.