A lot of exercise is supposed to help, as long as it is not too late before you go to bed. I have heard good things about warm milk. Supposedly the tryptophan released by the milk puts you in food-napping mode, but it's never worked for me. If it gets really bad, you could try melatonin dietary supplements with dinner. These trigger sleepiness in many people.
Those are all just general practice stuff though. Is there any reason you can think of that this would be happening?