Hi, I Have Had Many Different Symptoms Over The Last

Hi, I have had many different symptoms over the last month and don't know what is happing. Firstly tight chest, so I went to the doctors and they said my chest is clear. Next day pain around heart, I then went back to doctor and had an ECG and many other tests, they all were clear so I went to A&E. They tested my blood and again all clear. Now I an experience light headedness, tightness in back of neck as if not enough oxygen is getting to my brain, fatigued and diarrhoea. Can you help?