Health problems resulting from anxiety can themselves contribute to your anxiety and make these symptoms worse. I've experienced something similar to you, with different symptoms. Long story cut short, I had symptoms, saw a doctor who told me I was perfectly fine but that my symptoms likely resulted from anxiety. I went home and started getting worrying about whether I had a terrible disease that the doctor didn't know about.
The problem with this kind of thinking is that we don't pull ourselves out of that anxiety cycle. Rather, we just give ourselves more things to worry about which just worsens and prolongs our symptoms. Meditation, like P0L0 suggested, is one thing you can try to relax yourself. Along with it, I'd also suggest downloading a mindfulness app like Smiling Mind and doing these exercises daily. At my worst, I did it three times a day. Another thing that helped me was to question my beliefs - that is, to question myself on why I thought I had a serious disease. Our bodies go through good times and bad times. Our digestive tracks are incredibly sensitive - honestly, it takes just one bad meal for us to suffer the next few days. Unless you have a concrete reason to believe this is really something worse (e.g. a family history, irregular blood tests etc.), the most likely explanation is anxiety.
Do the mindfulness and meditation exercises for a week or two. Try to consciously relax your body and clear your mind. Tell yourself there is nothing physically wrong with you. If it helps, participate in activities that distract your mind (e.g. exercise, painting etc.).
I hope you feel better soon.