Can you get muscle strain on the stomach from doing sit up?

I recently doing start doing sit up after a meal in hope to lose some weight, i do 30 sit up after 3 hours of eating and i do it twice a day. It was fine on my first day but i get a light pain sensation on my stomach and think it was probably nothing but on the 2nd day, i start getting this pain on my upper stomach and when i tried to do sit up, it hurt really bad. Did i strain a muscle from over doing it or it is something else?