Hey, it’s good to visit a doctor, a traumatologist for example. This is just my experience, I’ve had tennis elbow diagnosed in the past and putting some ice for a few minutes after playing when it has been intense has been good enough for me, they might also recommend to do some form of rehab either at home or at with a PT. Another thing in my case is that since I learned that my primary motion is DSX I try to use it as much as possible, and that has reduced a lot of tension and incidence of tennis elbow. I always tried to do pentatonics like EJ starting with a downstroke, it never worked fast and it created a lot of tension, now I do it like Andy James starting on an upstroke, now I only do USX string changes as a secondary or helper motion and I also try to avoid it on even numbered groupings specially on pentatonics (since you pretty much have no choice but to do either USX or DSX at fast speeds, it’s really hard to get a secondary motion going in there) and also on 4 notes per string even though my secondary motion has gotten good enough where I can do four notes per string at decent speeds with USX string change but again it’s just easier, more natural and faster doing it with DSX. Another thing is that I had to polish some details and movements in my technique, I’ve been using some of @Tom_Gilroy ideas for the fretting hand, specially the power grip and it has been great and also the wrist motion tutorials on Primer to do a proper picking hand motion, I used to do ulnar deviation and that just creates a lot of tension .
I’ve also had golfer’s elbows and cubital tunnel syndrome but they weren’t necessarily caused by guitar but from other physical activities, now I just do some daily stretching and mobility of wrists hands and forearms and just a bit of strengthening of the forearm msotly extensors in my case, to prevent the injuries from re-appearing. And I train my body with bodyweight strength training 2-3 times a week, good for posture, strength and staying healthy,can help with grip stength aswell, you can do any sort of strength training that’s also good for mobility, or add some mobility and flexibilty separate… Don’t want to overdo it since that can also cause injuries and affect guitar playing aswell.