Feeling sick/cramps but not on my period...

Last night I ate Chick-Fil-A on my campus with my boyfriend and within a few hours my stomach started hurting with a almost stabbing pain- really bad stomach cramps. I went to the bathroom and felt a little better and eventually fell asleep. This morning, my stomach continued to hurt and cramp, as it has all day. I've had diarrhea a few times but no blood or anything abnormal. My appetite is the same, but I constantly feel like I need to be on the toilet. I also feel cramping in my lower back and my hips are very sore. Should I be concerned? Do these sound like symptoms of anything serious, or could it just be the food, stress, whatever?