The scratching an chewing of himself could be due to a number of reasons. such as dry skin; parasites; anxiety; maybe experiencing pain in that area etc.

but keep in mind young puppies pee a LOT. like 30or more times per day... its best to take puppies younger than 6months of age outside every 35/45minutes an right after he eats/drinks or wakes up from a nap. everytime right after he does potty outside give him a treat an lots of praise as you want him to associate that going outside = a good thing.

but if the peeing is indeed an abnormal amount for a puppy than it needs be looked into. UTI can cause frequent peeing along with diabetes an bladder stones etc.

i would say get him to the vet but its so much easier said than done with this Covid thing going around.
best of wishes to both your puppy an you