Pulsing under left collarbone and extreme fatigue and dizzyness

[sadmoh]

Hello,
It all began 6 month ago where I felt really weak and fatigue after a light workout session. After that I had no other symptoms till 4 month ago where I started to feel dizzy and fatigue in the afternoons. And this just if I was out of house and walked around for 2 or 3 hours. 3 month ago I started to have weird pulsing in my legs(calves) under the knees in both legs. This was also just in the afternoon and just if I was sitting down somewhere. When I walked, I didn't feel any pulse but the fatigue and headache and dizzyness were always there. When I got home and lied down a little everything got ok after 20 minutes or so.
These symptoms were ongoing till a week ago where the pulsing started under my collarbone in the left side and also a weak pain under my left arm muscle. I also feel extreme fatigue and dizzy all the time, no matter if I go out or not.
I'm a smoker, I'm  34 years old male, weight around 74 kg and am 178cm  tall. Please tell me what it could be.