What is wrong with my stomach?

Well my stomach has been hurting. Not that much it feels like a normal stomache ach. It hurts on the lower part of my stomach. I am not sure but i hear rumbling sounds i guess its like growling like when your hungry. I don't hear that every second but sometimes I do and once I go to the bathroom it feels better. It feels that feeling when your hungry also when you do sit - ups and you haven't done sit - ups for a long time and your stomach hurts. I am underweight. For sit - ups thats the feeling for the lower part of my stomach. On my sides they dont hurt as munch but they do growl from time to time. Is this normal also I have vomited but that's because I was grossed out of something and it was only once on Sunday. My stomach has been hurting since Sunday and today is Tuesday.