Could this be endometriosis?

For the past 4 or 5 years now (i'm 20) my menstrual cramps have become exceedingly worse, EVERY month. It's to the point now where I'll take 4 ibuprofen every 4 hours and still end up in my bed, crying. (and I don't cry over much). I also have diarrhea and constipation on my period, sometimes they alternate. I have what I like to call " cramps" which is like stabbing pain in my ... rectum, which occurs sometimes when i sit down and sometimes when i'm just standing around. It hurts a lot to poop while on my period. That pain almost brings me to my knees. It also hurts when i pee sometimes. My uterus also swells an incredible amount and feels like it could pop if anyone touches it. Recently, it's gotten so bad that it hurts to walk, breath sneeze or sleep. The pain radiates down my legs and makes me sick to my stomach. Sometimes I gag I'm in so much pain. I get my period every 25 days and it's lasts for at least 7, sometimes 8 or 9 days. When on my period, I have to skip school and work. I've been to 3 doctors (gynos) about this (and told them exactly this), the first two told me i just had some 'cramps' and put me on birth control, ponstel, and cataflam (prescription NSAIDs) at separate times, obviously, which did nothing for the pain. The most recent doctor I've been to, told me I was describing IBS to a T. It's getting to the point that I have cramps and pains throughout the month. I feel like no one is listening to me. I read about IBS and while I do have some of the symptoms, i have most, if not, ALL of the symptoms of endometriosis. I feel like something is awfully wrong and every freaking doctor I go to just smiles and tells me "sounds like you have some bad cramps" or "it's IBS!". Has anyone else had any experiences like this? Any advice? Please. I'm desperate. I will answer questions if you have them, I think I covered most everything though. This is by far the worst pain I have ever felt, and I feel like it's taking over my life.