Dodgy deltoid/shoulder muscle/wrist flexion?

Ive been having a problem with my left arm for years now. there no REAL problem in terms of pain however im sick of people telling me 'your left arm is MEANT to be weaker if your right handed'...even i know that but theirs muscle wastage on my shoulder, and my arm is smaller and weaker than my right arm. it also sits differently, i struggle to keep my elbow tucked in a normal position it sort of 'sits outwards' abit. also i struggle to flex my wrist and do a full curl. i cant touch my left shoulder with my left hand.also when i do bicep curls iv noticed theirs something in my deltoid that sort of flickers as i move my arm up and down.like a tendon? its between my shoulder muscle and chest muscle. theirs no pain apart from a lot of strain from even light weight ie 1kg.iv been to the doctors but they don't seem too bothered because theirs no pain...my left pec is also fatty, like gyneaomastyia or hoever you spell it!?...even my back has a small amount of muscle waste and the joint is generally A LOT weaker than it should be.i don't remember having any serious muscle tears or rips but iv left this problem like this for years out of having my time wasted but now i need to know whats wrong with it because its affecting my physiologically and physically because im getting over weight...any have one have any ideas on what the problem could be please?