revg

My gsp constantly pees in the house (he is 31/2 months old) he is potty trained well ...he goes when let out...he controls himself while we are away and all night (last out time is around midnight) then out again around 6am... but will pee outside and return inside and automatically pee when he gets excited... even after empyting his bladder outside... I believe sometimes he is just marking but intend to get him check out at the vet to make sure he doesn't have any medical issues... is there any one experiencing this with their german shepherd puppies? any advice... I don't believe it is a training issue...just don't know the answer to this problem need help.