What Causes Severe Pain In The Knee?

Hi, My left knee has been hurting since the week of July 10th. I think I may have twisted or turned the wrong way doing something. It gets to where I cannot even straighten my whole leg out and stand on both feet.It feels like it may be on the front towards the outside of the knee/leg area. Sometimes it feels like it may need to just pop too.I do have an appt on the 10th of august but wanted a little info before then. My husband thinks it could be a torn ligament. I do begin bowling in two weeks too and wanted to know if I should postpone that as well for now. It also gets to where I cannot even hardly walk on the leg. Any ideas?