Puppy Biting His Tummy

Hi I have a 6 month old black lab. The last week or so he is constantly scratching and biting his belly. I can't see anything there, it's not red or inflamed. I thought he was just 'playing with his bits' but it's more to the side of his genitals. Any ideas?

 

I would just take him to the vet. Mine was doing that and she has a bladder infection