Search recent threads with Golfer's Elbow, there are several. Very similar injury to Tennis Elbow(located on the outer elbow), so search those TE threads also.
GE is a tendon injury possibly associated with hitting forehands perhaps with certain grips and other tennis strokes. I believe serves also but I don't know why.
Super-Stupid Self-Taught Volley Technique -I got painful GE instantly when trying to add pace to my volley with a very bad technique and full force.
I can see where the name Golfer's Elbow may have come from:
1) When you accelerate the club - I'm not a golfer at all - I believe this tendon is under considerable tension.
2) Also, if you strike the ground during your swing the impact might put extreme stress on those already stretched tendons that come together at the origin on the medial epicondyle. Do you rarely hit the ground?
The injury could occur from bad tennis stroke technique or using good technique when your body is not conditioned for the stresses of the stroke. For example only, tight/short muscles in your forearm. Maybe these forearm muscles are OK for a golf swing but too tight for a windshield wiper forehand?
I got some light GE pain on my non-tennis left elbow several months ago moving awkward heavy logs. I stopped all stress immediately and now it is OK but I can still detect it on some exercises. Don't diagnose or treat your unknown injury of unknown severity based on anybody's experience on the internet.
VERY IMPORTANT - I read that stressing an acute tendon injury can lead to defective healing on the microscopic level permanently
. See my posts on GE & TE threads.
Stop stressing it and see a well-qualified Dr.