I just began my biking regimen over the past week. I have my bike fitted properly to me and it felt great test riding it prior to purchasing.

However, I noticed maybe not the first time out but this past ride of 20 miles that my shoulders felt strained at times... I'm wondering if it's just my muscles getting used to the position that my arms have been in? (never rode a road bike before this).

Or if it's a fitting issue?

Please advise. It's definitely not a crazy pain, it's more like a "discomfort'

Thanks in advance