how old are u?
don't be fucking stupid and listen to the 15yo's telling u to ice it and rest it, they're 15 and made of rubber and have no idea what they're talking about. people tear there acl's all time and don't know. my buddy tore his and just rested and iced for 2 weeks then kept riding for another 3 months, then landscaped all summer, then rode half a year, and it still hrt him some. got it checked out and his acl, and some other shit were completely torn, he was just tough about it and didn't do shit for 2 years.
go to a doctor, tell him to give u an mri, not an x-ra, it could be a number of things, knees are tricky things, and everyone has different symptoms. yes they are expensive but u don't want to find out that it actually was something torn 2 years later and have arthitis and pain in ur knee for the rest of ur life. u do want to ski for the rest ur life right?
if u don't have health insurance, ur just plain stupid. get some, and get an mri. a knee injury can usaully wait, but i wouldn't do any activity till then, and it can make the recovery longer.
go get it checked.