I treat my yorkie for fleas every thirty days with the stuff you put down the back that's supposed to coat his entire body using his own natural body oils and I bathe him regularly with a flea and tick shampoo. He still bites and scratches himself a lot. Could he still have fleas? He does go outdoors at least twice a day for walks. I was thinking of trying a more expensive flea treatment like frontline but I would hate to waste the money if fleas/ticks aren't the reason he's biting and scratching himself. What else could it be?

What are you currently using?

I use frontline for my dog and give her a bath every 2 weeks, but she still ends up scratching + biting herself every now and then. If it's not too often and not too severe, then I would just pass it off as him being a dog.

Perhaps at the next vet check, you can ask to check for fleas?

A simple way to test for fleas on a dog is to place it on a light colored surface such as a white sheet. Brush or comb the dog for several minutes. If any small dark specks are present on the white background place a few drops of water on them. If the area turns red, then the specks are digested blood (aka flea poop).
Also please be careful about mixing flea medications such as shampoos and topical treatments, since using more than one chemical may lead to toxicity.

There are a number of highly effective modern flea remedies. I have used Revolution on my dogs the last 4 summers and haven't seen a sign fleas or the flea dirt Carol discussed.

Bathing dogs is one of the most common causes of scratching and itching. The less you bathe the dog, the better. When you do bathe the dog, be very careful to rinse out the very last of the shampoo.

Feed a decent chow and as little else as possible, seldom if ever bathe the dog, and brush it daily with a soft bristled brush. If the dogs still has an odor problem, see the vet. If bathing it fails to eliminate the odor, it could be infected ears.

The best way to control fleas is one of the modern remedies, Advantage, Frontline, Bio Spot, Revolution, etc.

I bathe the dog once a week because he has really bad breathe from tartar build up. So when he licks and bites himself his fur starts to smell really bad and I have carpet which has a tendency to hold odors. I'm going to get his teeth cleaned soon but it's a bit pricey and I'm a bit broke right now. I just gave him a bath abd he hasn't licked himself once yet so maybe I wasn't getting all the shampoo out and it was irritating him. This time to rinse him I filled the tub with water and submersed his whole body, except his face of course,

Have you tried brushing his teeth? If not even brushing his teeth, wetting a cloth and wrapping it around your fingers and just rubbing his teeth and the inside of his mouth on a regular basis should help.

Been there done that, he will not let me anywhere near his mouth. I think it is too sensitive at this point for me to try to clean his teeth myself. He just won't let me I wish he would that way I wouldn't have to pay the vet. Also he won't eat any of those things that are supposed to help clean his teeth. I've tried all kinds, it's like he knows what its for and he won't go anywhere near them. Other treats are fine.

You know I have a yorkie too and they do have different rules than some other breeds. It is OK to bathe him fairly often because their coats are more like the hair we grow. It is not a normal "dog coat". This is why they are more sensitive to the cold and get chilled easily. I do not have a problem with fleas and I live in South Texas where we have them year round. I am not against chemical flea control but have found another solution. I sprinkle garlic powder in my dogs' food every night and it supposed to be a natural flea repellent. It either works or we are really, really lucky!
It sounds to me like your dog has allergies if you are not seeing fleas on you or the dog. My schnauzer has had allergies for 10 years and it is just something we deal with. When he goes through his "bad" stages I give him Benedryl and the rest of the time he seems to be OK. A dog will sometimes constantly lick and chew on their paws when they have allergies. I would ask your vet about allergies and about giving any medication but the general rule about Benedryl is 1mg per pound every 12 hours.
Hope this helps!