I'm a long time reader of these forums, and first time poster.....here's my story. About 18 months ago when suddenly I reached 300lbs and felt like **** everyday, I had enough. I went and bought a mountain bike from the LBS, and hit the road. Now I'm down to 240lbs, and have run into a problem with my knees. About a week ago after riding, I felt like the front of both knees were throbbing. I chalked it up to just overdoing it that day and took the next day off. The day after that while riding it came right back! No major pain, just a dull throbbing. So I took the next 5 days off from riding, which really sucked but I figured I'd better, then this morning I went out and took a real nice, slow, easy ride of about 12 miles. The knees felt a little better, just kind of like I had no strength in them. Came home and iced them and they felt fine most of the day. So am I just overdoing it and really need to take some time off? And is there anything I can do to make them feel better? Im pretty sure its not the bike fit, as I haven't changed anything in a year and half, I would think it would've come on sooner if it was. Now keep in mind I'm still toting over 200lbs around when I ride....but here's my basic schedule.
Mondays...12 miles, nice and easy
Tue...24 miles flat route, pushing it
Wed same as tue
Thur same as wed
Fri day off
Sat 40 to 50 miles on hills
Sun day off
This has been working pretty good for me as I'm definately losing the weight, I'm just wondering if by doing this I injured something? Any advice would be great!!!!

Knee pain from cycling can be have several causes.
1. Make sure your bike is properly fitted, if the pain is on the fronts of your kneew, try raising your saddle in very small increments

2. Are you mashing hard gears? Try spinning a higher cadence in an easier gear

3. Too much climbing can be murder on your knees, especially if your not properly geared.

When I have knee trouble (comes and goes a couple of comes a year), I take an extra day off the bike occasionally and when I'm riding, I just spin in my small chain ring for a few rides and stay away from the big climbs. If the pain persists or seems like something other than soreness, have it checked out

+1 for the above and some additional thoughts:

Be sure to stay hydrated. Dehydration reduces joint flexibility that can cause some pain during exercise.

Try to pay attention your knee action while peddling with the thought of keeping lateral movement to a minimum (knees work best in one direction).

Do not discount your set up as a potential cause. As you increase milage and effort, minor fit corrections can really come into play. For example, too low a saddle for a 10mile ride may not cause noticable discomfort, but on a 20mile ride it could really lead to screaming knees. Take a peak at Sheldon Brown's article on bicycling and pain.

Since I dont wanna make a new thread, i'm just gonna post my knee problem here too. When im riding ill get recurring knee pain only in my right knee, I've had a problem with it before, had a doctor check it out and nothing. And its only while im riding, and goes away after. I keep a high cadence of usually 85-100 which is comfortable for me, but when i start getting in my low gears and still keeping this cadence i get like a burning pain on the inside front of my knee, goin from top to bottom so its the whole side. And my left knee is fine...