Internal back pain and fatigue

About a month and a half ago, I started experiencing a burning sensation in my lower back. It feels like someone is pinching my insides. It spreads to my sides at times. It comes and goes throughout the day. When I first got the pain I went to the emergency room because I thought it might be something to do with my kidneys. They did a bunch of tests and found nothing. I went to a new primary care and he was confused and sent me to my gynecologist. I just had my son by cesarean in February of 2009 so I thought maybe it could be related. The pain is unlike a spasm or sprain, it feels really internal and burns. I saw my gyno and she did ultrasounds, pelvic examinations, etc. Found nothing. I had to return back to the hospital because it got more severe and then fatigue came on. They did an abdominal ctscan and found nothing, they said maybe the lower end of my colon looked a little swollen but maybe not. I then made an appointment to see a gastro doctor. When I went to him he was confused by the back pain and didn't quite see a relation. I've had severe constipation for the first time in my life so I thought maybe all this was related. Basically, my symptoms are severe lower internal burning back pain and cramping, severe fatigue, and constipation. I was put on a miralax regimen and it didn't seem to do much. I've even thought maybe it was hormonal and got on birth control. I've had blood work done, ct scan. Nothing has come up. I had a colonoscopy the other day and the only finding was a little inflammation on my small intestine and the start of an ulcer. The gastro doctor said that this could be related to the constipation I've been having. He told me fatigue is not related to digestive problems and I've heard differently. He thinks I'm just depressed. I'm 26 years old and really over all this. I'm becoming depressed because I'm always sick. I can barely take care of my son. I need some answers. Any ideas on what might be causing this. I'm seeing my new primary care next week. Thank you.