The high protein, low carbo diets can work pretty well for sedentary people. But if you are doing much riding, complex carbs and lots of them is the way to go (at least generally).

When I do high mileage, say 300+ miles per week, I keep my protein levels about the same, I tend to decrease the fat more because it is harder to digest and I eat lots and lots of carbos.

You may not want to change your diet drastically in a short time because it is working but you may give it some thought.

The advice to have yourself checked for diabetes is a good one. Diabetes is at epidemic levels. I have a friend who is a diabetic. He had to figure out what foods spiked his blood sugar. And apparantly, each diabetic has to figure that out by trial and error. Some foods spike his that don't bother other diabetics. Human metabolic response to individual foods seems to be ....... individual.

I went to a SPA some years back and they had a high fiber, complex carb very low fat diet with lots of exercise. I found myself getting very sleepy in the afternoons. My brother, who is ultrafit, said that he found a cure for this. He went out and at a grease burger once per day! Now I dunno, but stranger things have happened. In your case, it is probably not low fat that is doing it. It might be excessively low carb or even the number of calories.

You may want to consult a nutritionist on this one.