I really struggle to increase the weight on my upper body. I feel like I'm increasing strenght in my back, but my arms never never gets stronger.

My weakspot seems to be the outside of my shoulder, I fatigue there almost immediatly.

I've been working out for many years with FB, but it's just not working.

I don't work, so I don't have any unhealthy movement there...

I know it's important to have strenght, but I actually don't see why I should push through, it takes weeks to add a little and then it just stops..

Any suggestion?