Welcome to HealingWell!
I'm sorry to hear of all your struggles with your gut. Have you been scoped, either EGD or colonoscopy? I think both those would be a good idea considering your severe nausea and occasional bloody D. How about
being checked for H.pylori? You might consider being tested for Celiac's and lactose intolerance. All these should have been covered by your doc, no matter your (young) age. Please go back to your doc and/or get a second opinion elsewhere.
Hope you start to feel better real soon.