I have a two week old puppie and his bum is red. It looks to me that it is raw, is there anything I can put on it or do I need to take him to the vet.

How did you get a 2 week old puppy? Why is this poor young baby not with its mother? It's not nearly old enough to be away from it's mom and litter mates. It's not even old enough to be weaned yet.

Yes, the vet is your only option. This could be any number of things. It could be an allergic reaction, constipation, an infection, a skin allergy, worms, etc. etc. etc. You need a vet.

It needs its mum.. its mum would lick its bum to clean it! Unless you plan to do the same take it back to its mum.