What kind of knee injury could this be?

I’m trying to Google but that never gives a straight answer lol. I’m hoping someone can help me out with knowing what it is so I can give myself the proper treatment.

I went on a 3.5 hour hike with friends today. 2 hours in, the back of my knee was getting sore and tight and very painful and cramping a little but I kept pushing through it. We took a few breaks but Eventually I was limping it was so bad.

I was also wearing my snow boots for the first time this year so My body wasn’t used to them yet so maybe it caused me to walk different and strain something.

I’ve now been home for 5 hours and it still hurts to walk. And I can’t put the injured knee completely straight. Like it’s locked or something. If feels really tight at the back. Any ideas? I know ppl are gonna say I should go to the doctor. if it’s hurting by tomorrow maybe I will. I just don’t wanna go for something that’s not urgent ya know?

Anyway, let me know any advice/treatment, ideas of what it could be. Please be nice 😊