Up your calorie intake to about 1500, keep your carbs in the morning hours for the most part, and your proteins in the afternoons. Don't eat after 9pm. I would suggest doing more pushups, say like 300. I would also suggest running in the morning, and doing like a set of 60 pushups before you leave, and a set after you get done. Your not going to gain much muscle mass without weight lifting, but you may be trying to lose weight, depending on what your current situation is. The rest of your program isnt to bad. I would try to change it up a little bit each day, concentrate on doing more pushups then situps on M,W, F and concentrate on doing more situps on T, TH. Stuff like that to keep it interesting. Write down everything you do everyday. Make goals. Daily, Weekly, Monthly, Yearly. Goals are what get us from one place to the next man. You have to be staring at something, striving for it, making it your life. Without that, you won't be able to continue your training for long periods of time, because then you will eventually become like 99% of the population and except mediocrity. Its a lot easier to watch ESPN then to put in the hard work to someday make it possible that you could be the one they are watching.

And man it's only been 3 weeks. It takes time to get gains. They don't come overnight. The only place success ever came before work is in the dictionary.