Sore elbow - Poor posture? Poor technique?

Hi, Lately - past month, I've been having a sore elbow. I think it maybe posture at work (I'm in an office at computer all day), but I have this constant "niggle" in my right elbow. Now when I go to practice dulcimer it really bothers me and I stop playing and stretch frequently.

Has anyone had this trouble and how did you solve it? Am I strumming/picking with poor posture or poor technique? Do I need to restring my dulcimer in the reverse and learn to play left handed (strumming with left hand, fingering with right)? I am a southpaw, so I suppose it's doable but I dislike the idea of starting from scratch again.

Is there any advice or even you-tube videos on correct posture & technique etc to avoid an achey elbow?

I'm not old enough to be falling apart!