Hi Garycelt,
Thanks for keeping us all updated on Harvey, as it must all understandably be worrying you.
To help with keeping little Harvey from jumping around too much, i would put him in a room which doesn't contain too many jumping games, i.e. a kitchen. As long as he has his toys and his bed he should be fine. You can buy puppy play pens, which may also help you - they have some good ones here
http://www.caninekennels.com/~sa_webapp/run.asp?page=3580
With regard to weight, i have just checked Bradleys vet book, and he weighed 14kg at 4 months old. This doesn't necessarily mean that Harvey is overweight, i know all Labs are different sizes and different builds. It may however help you, if you cut down his food a little. Did you vet suggest that at all? I know that when Bradley hit 6 months old he starting putting a few extra pounds on, so we halved his daily food intake. Our vet advised us that the guidelines on his food (Purina Pro Plan) were simply that, a guideline only, and sometimes the recommended daily amount could be a very generous amount. I think it's always best if they are a little under rather than over, weight wise, when they are really young anyway - what with all the running around they do, and occasional health problems that can arise.
Has your vet asked you to take Harvey back to see him again? Did they do any X-rays?
If it was me, i would probably give the vet a call and mention the recent limping in the other leg, see what he says. Also, have you contacted your breeder? They maybe able to help and advise you.
I also found this article when searching for more info: (Might not have anything to do with Harvey's problem, but thought you might like to read it anyway)
http://www.geocities.com/Heartland/9911/pano.htm
Try not to worry too much, i know when our Labs are unwell or have a problem, we do worry - but we all care about little Harvey, and i'm sure the problem will right itself, or you will get some more answers soon.
Keep us posted.
Bye for now
Julie