You may need to really clean up your diet and remove any possibility of cross contamination and hidden gluten. It doesn't take much gluten to turn the immune attack on. Can you switch to eating only whole foods for a few months and see if it helps? I assume you are doing the cooking yourself also. If not, you should start doing your own cooking. And not eating out at all. Have you checked all your vitamins and meds for gluten?
There are only a couple possibilities that I know of. Either you are still eating gluten in some way, possibly very small amounts you aren't aware of, or you have refractory celiac disease. Refractory celiac disease is rare though, it is much more likely you are glutening yourself without realizing it. A gastro can't tighten up your diet, only you can do that. I hope you figure out the gluten source soon and eliminate it. If there is a lot of baking in the kitchen you share, that could be a major cc problem.
By the way, with positive antibodies and a positive biopsy, there is no reason for the gastro to say you don' t have celiac disease. That just doesn't make sense. It's a good thing you are changing gastros!