Knee pain but not sure on diagnosis?

I am 15 years old and i play tennis alot. I the last 2 years i have had reacurring knee pain below my knee cap, i went to a physiotherapist and told her my symtoms and she told me i had patella tendonitis but since then the pain has spread to the side of my knee as well. Is it still patella toendonitis or should i go back to the physio?? Please help!!