Hummn, if grodanboll is in Sweden, I know why he is not going to doctor. With non critical injury he will wait months for help.
If so find a private physiotherapist to take look. You probably just stretched everything out. Take some ibuprofen for 5 days, stick to walking.
Start riding a bicycle to build knee strength.
Ive been cycling 38 years and just crappy amateur. Its kept my knees in good shape and at 54 going strong: kiting, skateboarding, rollerblading, snowboarding, cycling.
But collided with a cat yesterday on bike and crashed. Had to go to hospital, nothing broken, but shoulder F-Upped. - 38 years without a crash...