My knee is killing me...HELP?

ok all of the sudden ( i dont remember doing anything to strain it at all) my knee hurts the surrounding area of my kneecap. and it also hurts behind my knee on the back of my leg. whenevr i excerise it hurts and when i sit criss-cross it starts to hurts. what is wrong with my knee?i dont want to see a dr. because im scared ill need surgery. HEEELLLPPP!