I had a very bitey, mouthy puppy. If you go to my page and read some of my old threads, you'll see a lot of great advice from people. My dog is a BC/American Eskimo mix, and some BC's are just a little mouthy. Here's what worked for me:
1. Sharp inhaling or gasping got his attention much more than "ouch!". If he bit me, I would inhale sharply.
2. Then, I'd redirect him to an appropriate toy.
3. If he bit me again, I'd inhale and redirect again.
4. If he did it again, that was "3 strikes". I'd inhale, and leave his penned area for 30 seconds - 2 minutes.
5. I'd come back and play again. If he bit me again, I'd leave again.
6. Finally, if I came back and he bit me a third time, I would put him in his crate. But not in an angry way, we used to call it his "relaxation station" and I'd tell him it was time to relax. He'd stay in the crate for 5-10 minutes.
Also, move slooooowly around your dog. This was the best advice I got. If he started getting riled up by my pant legs, I'd move very, very slowly and he would lose interest.
Regarding the petting, my dog, who is now 2 years old, only now allows us to pet him without nipping for the majority of the time. He still nips a little. The method you're using is good, just know it takes time for them to calm down. I would hold treats or kibble in my hand, pet him 2-3 times, then give him one piece while using his marker word, then return to petting 2-3x, marker, kibble, etc.
Finally, your dog's biting may decrease as he goes through the teething stage. My dog's biting and hyperness got really, really intense when he was losing the last of his teeth, and after that was over, he calmed down a little and his biting decreased a lot. That happened between 5-7 months.
Good luck! Your dog is adorable btw