Hi... The stiffness and popping in your knee could be due to imbalance of muscles around the knee, especially tightness of gluteus and quads led to uncomfortable positioning if your knee cap...leading to stiffness and popping.. I would suggest you to Keep a icing your knee 3-4 times I a day for 15 mins.. Gently stretch your Front thigh muscles by bending your knee and touching your heel to butt...take it as far you can if you are not tolerable or flexible.. for gluteus stretch bend your knee place your keg on a but high platform and try bending forward..... Gently knead above the the knee and around the patella to reduce the spasm and stiffness... once your knee becomes comfortable...then do bridging... clamshell...step ups... Hope this is helpful for you... Revert back in case you need any further clarification..