Pain between ribs left side, under armpit and radiating whole left side

[Leo118]

Hi, Im 31 year old male. Born few months prematurely and never caught up so little underweight and on the thin side but not unhealthly by any means. First noticed pain when I was 15 years old and doing press-ups with a friend, felt dull ache on left side of chest. This pain has been there ever since and I've just learned to live with it but I have only recently started worrying that it might be serious. The pain in intense in between my left ribs and underneath my left armpit - if I push my thump deep into my armpit I can localize the pain, its so intense, feels like my nerve or something. The pain radiates to my back right underneath the shoulder bone at the back and some down my left arm. Comes and goes in waves, can be ok for months then it will hurt for weeks. If I lay down a certain way I get a very sharp pain and have to jump up - it's very odd. Pain is really bad actually in between each rib on the left side. Any one got any ideas?