You need to see your vet and get an evaluation and a referral to ACVS board certified surgeon/orthopedic specialist. That is the only way to know what is going on for sure. It could be that the LP has gotten worse or he could also have torn a ligament. If it goes on much longer, the meniscus will also be injured and worn down and then he will have no cushion left in the joint and it will be bone on bone and he will be lame. His limping demonstrates that, in fact, he is already in pain. Please take him to the vet.
https://www.acvs.org/