I know what you mean. I used to practice a hole day before, and after a while I got sleepy, and sometimes I even slacked off. But after practicing that much, I decided to make my training session smaller and I got to tell you; I feel much better, and it actually helped me improving my fitness and I can run much more in games. Now I am in a off-season, with team training but no serie matches until about january-february, and I decided to go back to a long session training because I am very curious of improving, just like I was before. What I am training to tell you is that, your body is getting tired and that you should do a small session with only 2-1:30 hours of light training each day until you start feeling in shape again and then you can go back to a longer session. Just rotate when you feel for it, and it all depends on how much you want to improve. But there is no need to do this if being sleepy doesn't infect your training session, like slacking off etc. Also if you practice like 3++ hours everyday, try to practice from monday to friday while saturday and sunday you just kick the ball on the wall or something. Just try to take it easy sometimes. I hope this made sense
A tip: Try to take a long special run once or twice a week instead of playing football that time. 1-1.30 hour(s) running.
p.s Don't sleep too much and don't sleep too little, because both ways will get you sleepy.
Or either its a serious health issue wich I have seen before