Terrible abdominal pain?

When I was pregnant with my first son in 09 I started getting this terrible pain in my abdomen. It usually lasts about 20-30 minutes straight and on a scale from 1-10 its a 12. I've had 2 kids and this pain feels worse than giving birth, in fact, it feels like something in my stomach is squeezing so hard its about to burst. The pain is mostly right under my ribcage where they separate and it spreads to my back. I've been to the ER for this matter about 3 times and never got treated or diagnosed with anything. In fact,they kept asking me if I was taking illegal drugs and I got very offended cuz I've went there 3 times for the same problem and they wouldn't even take me serious. Anybody know what this could possibly be? A friend said it could be ulcers,I'm just asking on here cuz my insurance was temporarily cut off and I had another episode today but I don't wanna go back to the hospital and have to pay another bill for nothing.