I dislocated my patella at the start of last year due to trauma. It was painful initially and the doctor referred me to a consultant who prescribed physio. It would settle and then flare for the next year and then start of this year I popped it out again and have done so 3 times since
I think you need to get your knees looked at and ask for a referral. It takes forever and I almost paid for a private MRI but mine is currently behaving itself.