She could out grow it
My Lab who is now just under 2 years old had an issue with one of her back legs when she was a puppy (about 3 - 4 months old also). Every time she ran it looked as if her knee or .. middle leg area would pop out of place with every gallop. I took her to her regular vet and he said she was too young but its not good, can only wait and see. Of COURSE I couldn't just wait and see I took her to a specialist and he said its nothing bad she'll out grow it. Her ligaments (I hope that's the right word) around the knee area were lose and as she got older they would strengthen and tighten up. I took it upon myself to not let her "over do it" with running, it seemed to get worse after alot of play and running around and by the time she was 8 or 9 months I barely noticed it. Now at almost 2 it's totally gone.
I'm only telling you this story, because everyone who saw her running told me horror stories about what my pups future was going to hold.
The specialist I took her to said very rarely do you see signs of hip or knee Dysplasia in puppies this young.