You are over exhausting yourself. You do not need to do that many sit ups. I recommend (and this works trust me) doing 50 sit ups and 50 crunches a night and in the morning, the morning ones aren't needed but they help jump start your body. Eat some protein, drink plenty of water, and you should be fine and start seeing results in about 1-2 weeks. Hope this helps friend.
Football 7 Yrs and Baseball 5 Yrs ... All required excercises and work wonders my friend