I missed a stair and stepped down really hard

Sorry to hear that. I hope you're OK.

Missed a stair and jammed my leg up into my hip

Sorry to hear that. I hope you're ok.

The pain started mild but has gotten worse and now I am limping. It hurts at the top of my leg

We can't tell you what's wrong based on that, nor even if you write a whole page.
Simple muscle strain all the way to torn tendon, meniscus, synovial fluid sac, cracked bone, you name it. 'Top of my leg' isn't much help either.
Usually you soak in a warm bath, move your leg gently as much as possible to keep it flexible, rest, use ice if you see swelling, and heat if you have pain, and see a doctor after a few days if it doesn't get better, probably for an x ray. But a lot can go wrong that doesn't show on x ray.

Most likely a doctor will just tell you to walk it out. It could hurt days or weeks