Tyr started in puppy kindergarten in Petsmart, then we proceeded to a basic obedience through word of mouth-check at your doggie parks-the best people go to them and they can often suggest a good trainer, also-your vet or the local petshops. always ask to "sit in" on a class before hand to see if the trainer is one you can relate to.
I'm not sure if you need to go to a class-maybe a private trainer. But always be there when your dog is in a training class-Most professionals agree-dog training is to train the owner to train their dog, not just to train the dog. But potty training is something that maybe suggestions would be best. Maybe to have a trainer come and "overlook" your methods and give advice. Or asking a vet for advice might help a lot.
Sometimes it's something silly you aren't doing right, or sometimes the pup just isn't ready yet, some take longer. And then-not to scare you but sometimes it turns out to be a medical problem (bladder problems, etc.)
There are also lots of great books out there.