I had a mcl tear in december and i sat out for a month. now when i play it sort of locks up and cracks but doesn't hurt for long. what could it be?

PES & hamstring: While there could be a number of causes including underlying cartilage damage or arthritis, your description sounds like a very common occurrence after mcl injuries. Likely you have hamstring tendinitis and pes bursitis. It is inflammation around the inner portion of our knee under the mcl that occurs with deconditioning of the quad muscles. Avoid limping and work quad exercises to improve this.