Knee pains

Patient: I have been having knee pains and problems for about 3 years and I’m only 16. The last few months have been fine. But, lately it seems every time I bend my knee it hurts. My mom told me I woke up crying the other night because my knee hurt. But I don’t remember. It hurts mostly when I wake up or if it’s bent to long or if I stand to long.. Andy to longi mean like five to fifteen minutes. It’s been going on for a week now. Just non stop pain. Someone also told me I might have water under my knee. I’m 16 I don’t want to get surgery what do you think it is?