Hello, 35 year old male here. Back in late 2019 I started getting sharp stabbing pains in the left side of my chest just under my breast?

and almost reaching my armpit. It was on and off. I went to the doctors who gave me some naproxen and it seemed to go away for a while. 

Then in about February/March last year it came back again, only this time it was more of a dull ache which varies in intensity, and it is also constant, there all the time, and it’s been there ever since. Ive had an ecg, blood tests, x ray which have shown nothing, I’m due to have a ct scan soon but they seem to think it won’t show anything and think the problem is probably something muscular due to my job which I spend a lot of time heavy lifting.I did think of costochondritis or something. Similar but The only thing is, I don’t have any shortness of breath, it doesn’t hurt to breath or cough, I don’t have trouble sleeping, I don’t have trouble moving my arm or no mobility issues, the only thing that seems to aggrevate it is doing anything strenuous. So if it’s muscular then why don’t I have any tenderness in the painful area, why does it not hurt to breath or move around? And why is it not getting better? The doctor said it could be due to lifting at work but I have stopped doing that for the last 4 weeks and there’s been no improvement. If someone has any idea at all I would be grateful for some info as I’m currently getting nowhere and I’m getting anxious that it’ll never go away. I should also say I’m quite an anxious person but surely stress wouldn’t be causing this as it is quite painful and it’s been going on a while now. 

Thank you