That sounds awful.
This happened to me once, I was having a flare but all my bloodwork was coming back normal - I finally insisted on a colonoscopy (like anyone wants one willingly unless they need it, right?) and once my GI dr had a look inside he saw all the inflammation and ulcers and said he was sorry he didn't believe me (I'm paraphrasing here ;) ) It turned out the one blood work test, which he had said they exhausted all tests, was the one that showed if I was developing antibodies to my Remicaide, which I was. So the medicine wasn't working and it was like I wasn't taking anything at all. They put me on Humira and after the painful flare subsided over the next few months I was better. I don't know what test you need but don't doubt that you don't know what is best for your body. Drs these days really aren't the experts and there are too many moving parts for them to keep up. Be the squeaky wheel with your health and if this dr doesn't listen to you then find another one who has more compassion. Good luck!