Upper back pains

Hey folks, first time poster, long time lurker…

I’ve had a long standing problem where maybe 45 minutes into a run or bike I start to develop mid upper back pain worsened by turning my neck from side to side. It seems to resolve if I stop and do a bunch of mobility for a couple minutes. I feel like I’m in general a flexible person but admittedly am not exactly strong in my upper body. I’m in my first year of really committing to consistent training and it doesn’t really seem to be getting better.

I’ve been trying to do a bunch of mobility stuff and I did get a professional bike fitting but it still seems to be present.

Would upper back strength training improve this issue? I thought it would just get better with more swimming but alas it’s not that much better. It would suck if this was the reason I couldn’t do an Ironman but it really does hurt bad when it happens.

Thanks for thoughts!