My knee keeps popping in and out and it's kinda painful. What should I do for it?

I went to the chiropractor this morning for it.
I have no idea what I did to it. The only thing I can think of that could have done this is that I fell on Tuesday while I was running. But it only started hurting last night. I would think that if that’s what I did to it, it would’ve started hurting earlier.
I have wrapped a towel soaked in warm water around it. I have used a heating pad. Is there anything else I can do?