Severe Anxiety, Palpitations, Chest Pain. Suggested To Put Holster Monitor To Check The Heart Beat. Burning Under The Sternum. Stomach Related?

I have been experiencing severe anxiety for about three months. Horrible chest pain , palpitations, etc. after 4 e.r. Visits, 1 cardiologist visit, and one other dr visit, all tests were normal except one blood test 1 time my d dimer was a little high but the dr was not concerned. I ve had an MRI, chestnxrays holster monitor, Etc. I eat very well and do low grade triathlon training. Doc is now going to put a 1 month monitor on just to make sure I don t have an irregular heartbeat . Why does my chest hurt so bad? Right on the left side it burns right under the sternum and then sometimes I have pain down further. Is it my stomach? I m so worried, am I just having a lot of anxiety? Had no issues a few months ago before the stres started. Now I m obsessed with my heart and all these weird pains. What isnhappeningnto me?