Some soft tissues injuries can take up to 6 weeks or sometimes longer to heal. And that healing is often dependent on the kitten staying quiet - no jumping or running! If an x-ray wasn't taken, this could be helpful. Sometimes there can be a hairline fracture or fracture of a growth plate that may not to be palpable on physical exam. In some cases, a small fracture may not show up on an x-ray right away. After this long, I think it is definitely worthwhile to try to figure out exactly what is going on. I would contact your veterinarian and have your kitten re-examined.
More...
My kitty is 22 weeks old and I notice that she is limping in her left back leg. She's 
Linear Mode
