all puppies will lose their teeth as they grow older and bigger. think of it as a child losing his baby teeth to make room the adult teeth...in dogs, their teeth are like sheaths when they are a puppy so that as they grow, the outer tooth falls out and is replaced by the permanent tooth. we normally don't see the teeth as they tend to swallow them, but when we do it can be cause for concern because we don't associate a puppy with losing their teeth
All dogs have puppy teeth, and at 5/6 months of age, get adult teeth. It probably IS uncomfortable -- that's why they chew on things when they are puppies -- they are teething. What exactly are you worried about?