Teenager with chronic knee pain, don't know where to go next?

[ckviolet5]

I am 17 years old and I've been having chronic knee pain for almost 5 years now. It started in my left knee and for the past 2 years it has been in both of my knees. I am an athlete and have played basketball, volleyball, and softball in the past 5 years and am currently just playing softball. My knee click and pop and lock in place on a daily basis. I have gotten multiple x rays and MRIs and they have all come back with nothing obviously wrong. I have gone to physical therapy multiple times and nothing has worked. My parents spent a small fortune on an electro-stim treatment that was supposed to almost eliminate my pain and it didn't work. Currently I have an appointment set up to try and get a blood test to see if it could be arthritis but if it's not I don't know where to go next. I don't know what options I have and I can't keep living in contrast pain for the rest of my life. Any input you could give would be greatly appreciated. Thank you.