Welcome!
I'm pretty new too, but here is my 2 cents: Are you increasing distance? I think you'll be able to tell over time whether it is about bike fit or conditioning. I have to say I have had a bit more trouble with shoulder pain this year than I seemed to last (and this is only my second year), but I had a long winter off the bike and it seems to be improving; that is, it sets in later and later as I increase my distance, which suggests to me that for me it's about conditioning and not fit.