Stomach cramps, very bloated lower stomach, back pain.

Hi, I'm a 18 year old female and for the last month I have been suffering from bad stomach cramps and pain ranging from my left to side up to my ribs. I have also been constipated or had dierhea with a feeling like I need to go but often can't. My stomach gets exteremely bloated (especially after I eat, but it is always to some degree) My back pain seems to center around my lower left side near my spine but can travel. Anybody have any idea what this could be? I have thought possibily of pregnancy, I had sex three months ago regulated by birth control. I skipped a few though earlier, so it may not have been effective. He pulled out, which again is not completely safe. I have had three normal periods at normal times and no other symptoms. I have also though of Celatics disease, as my aunt has this and I feel especially bad after eating. IBS has popped into my mind as well. If anyone has any ideas, I would love to hear them!