Fluid filled lump on left part of right knee. hurt to touch. next day lump is gone but it still hurts to touch. any ideas of what it could be?

It might be bursitis: blister or a hemtoma, based on the fluid-filled feature of the lump. Did you hit your knee recently or do you spend a lot of time kneeling? I would apply a cold compress to it and take Advil (ibuprofen) for pain if needed. If you start to have increasing pain, difficulty walking or develop fever, I would see a doctor right away! Feel better!