Left pain please help!!!?

Ever since I was about 10 I’ve had difficulty go to the bathroom. I constantly get severe stomach cramps. I’ve been to the doctor but they just say I need more fiber they don’t do any tests what so ever. The fiber they prescribed upsets my stomach worse. Also taking stool softeners or laxative upset it too, & they don’t help at all. I’m 19 now & 9 months ago I had a son. Ever since it’s been getting a lot worse. I get extreme pain on my left side by my hip and also right below my left ribs. It also seems like if I eat it causes a major stomachache and I feel like I’m going to throw up. Also, I’m thirsty 24/7. I mean I can drink like a big thing of Gatorade and still be thirsty. The pain is getting worse and worse, I want to go to the doctor but they just keep telling me it’s nothing all it is is I need fiber. What could it be? & What can I ask my doctor to look for or do to actually look for something wrong? My bf keeps asking if I feel ok cuz I don’t look ok & he thinks Im pale.