Welcome! I'm glad you've found us here, as this is a very supportive forum.
The questions you ask are typical of many of us. Of course, only your doctors can give you a diagnosis.
Regardless of whether your symptoms initiate from anxiety or are caused by something else, it's easy to develop anxiety about
your health when you're feeling uncertain. My own experience is similar to yours, and it took me months of asking my doctor what could be going on and what possibilities he could rule out before I came to grips with those symptoms that were anxiety-based and those that did come form another, benign condition.
Try to remind yourself that if your tests have come back negative, then you can reasonably trust that you don't have the condition you fear. (Of course, that never stopped me from finding other conditions to fear!)
My advice is to continue working with your doctor to get some satisfaction about
your diagnosis. (My own opinion, I'm not a professional.) You mention several digestive symptoms; have your doctors ruled out those kinds of issues?
I'm sure other members will be along soon with more insight.
Co-Moderator, Anxiety and Panic Forum