I Have Been Experiencing A Nagging Sore Upper Tricep (right

I have been experiencing a nagging sore upper tricep (right arm) into my shoulder area a bit over the past 6-8 weeks. I have good ROM, and seem to be fine structurally, but continue to be sore on a daily basis. It wakes me up at least once per night. I do not remember an event that triggered it.
I am normally relatively active: run 3 x's/week, work out (not heavy lifting), in a cross-fit type class 2 times/week.
Thank you.