I Was Excersizing The Other Day, And Felt A Pop

I was excersizing the other day, and felt a pop in my left knee. When I went to grab it I felt a lump or knot and I moved it over towards my knee cap and the pain went away. The pain is not constant, but I will move the wrong way and feel pain again. The pain is so bad to the point I can't move my knee. After the pain settles within a few second I'll feel the lump again when ill try to move it around until I feel whatever it is, is back in place. Not sure if it's serious or not just hoping I could get some insight of my situation if there is something I can do about it or not.