Odd knee injury, help?!

Alright, a few days ago, maybe even a week, I fell forward on some really hard stone steps and my knee hit directly on the corner edge. It left this almond shaped wound that doesn't look anywhere near as bad as it felt. Anyway, the second day, it developed this yellowish colored ring right around the edge, so I thought it might be infected and put some hydrogen peroxide, antibacterial cream, then a band-aid (that didn't stay on). The ring is still there, but it doesn't really look like an infection anymore.

It's raised, almost like a blister that's hardened, and the center is scabbed over, but the ring is now turning a dark red. I thought it was scabbing, so I don't understand why it would be raised or why it would change color like that.

Also, my knee is still sore and hurts when pressed against, kind of like a bruise, only much more sensitive. When I walk for a while, or walk fast, it gets sore and I feel like I need to sit down but can't sit down too fast or else I risk it hurting more. I haven't seen a doctor about it yet because I didn't think I would need to. But now it's becoming quite an annoyance and certainly doesn't feel good, so I wondered if there's anyone out there that has an idea on what I should do.

All help is greatly appreciated and sorry for the wall of text.