Knee Pain

I think I've screwed myself slightly

I've been off the bike for a couple of months after going on a massive ride and ending up with pain in my left knee, got back on last week and just did my commute once and I think I've over extended my left knee again, as it's now really sore down the back on the inside

Going to try and get it seen to ASAP, but anyone know of anything I can do in the short term, I'm staying off the bike for now

Pain directly behind the knee (i.e. the bendy bit), on one leg?

Snap- I find that hamstring stretches make it ease-off, and [birnie]smashing it[/birnie] brings it on