5-Year old Yellow Lab limping

Question
He weighs about 97 lbs but he is a big dog too.  The last 3 months he hasn't been getting enough exercise/walk as he usually does since my wife was out of the country.  I will stay in touch with the vet as you had suggested.  Should I ask the vet to take x-rays of his front legs also?  Also should I take him for short walks even though he is limping? I don't want to harm it anymore than it is now.  He is not squealing in pain anymore and his bark is back to normal.  
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-----Question-----
About 10 days back all of a sudden, I noticed my 5-year old yellow lab limping and was even squealing at times.  We were certain that it was the left hind leg.  I had to board him with my vet for about 6 days since I had to leave town.  During that time, they took x-rays of his hind legs and found no problem.  After I picked him up last week, now I feel that he is limping on his left front leg.  He is a very healthy dog and eats well.  He is able to climb the stairs.  But his limp remains.  Any thoughts?
-----Answer-----
There are some things like muscle strains that go away eventually.  If he is favoring his hind leg, he could end up stressing the front.  I would continue to stay in touch with the vet if it doesn't get better.  

How is his weight?  Not only do overweight dogs not live as long, they have more joint trouble.  Check http://www.puppychow.com/products/popup_body_condition.aspx and cut back on his food a little if you need to.

Answer
Check his ribs as the link explains.  Also he should show some belly tuck up as shown in the one side view.  I got caught on that one a month ago.  My Holly came to me at 7 weeks over weight.  At her 11 week evaluation by the professional field trainer, she pointed out Holly still had too much belly.