My experience with tennis elbow is weird... the pain showed up in 2017 and lasted into 2018. I stopped throwing entirely for weeks, with brief rounds to see if the pain was gone. And it was sporadic. Sometimes I'd be good for a week, and then it'd return. Sometimes a few weeks of rest did nothing. After a while I started to look into other things I was doing in life, because although I spent months thinking disc golf was the problem... well... maybe it wasn't?
Ultimately, after weeks of trying to remember to reflect on my injury any time I was doing anything with my arm, I realized that when I played tug of war with my 20 lb dog I was allowing serious stress to be put on my elbow. I was doing that thing where you just grip the tug toy and let the dog whip it and your arm around. I would just let my arm hang loose, and he'd go to town. I thought it was harmless - light weight doggo, arm just dangling, can't be too much stress... and I was totally wrong.
As soon as I stopped playing tug of war like that with my dog the improvement came. Within a few weeks I could feel a difference. Within a few months it was like I'd never been injured.
Maybe this doesn't apply to you. Maybe you can be absolutely certain your backhand is causing the issue. But if you haven't taken time to rule out other causes you should take a little time to reflect on what else you're doing that might seem innocuous but puts stress on the elbow.