What if you did some other activities while you sort it out? Like lower weight, more stretching, etc...?
I, in no way, can diagnose it. All I can suggest is to try different things until it feels better.
I had a ache/pull/pain in my hamstring a few years ago. I suspected it was from running. It sounds similar to yours. I was pretty diligent in rolling it out. I kept a lacrosse ball in both vehicles and would roll it around while I drove. It eventually got better.
Hope it works out for you soon.