Puppy biting

I need some serious advice! I have a puppy who’s 5 months old, she’s a lab pit bull mix. For the most part she’s a really good dog, however her biting is an issue. She’s not aggressive by any means, but whenever I pet her she tries to bite my hands like they’re toys. And it’s not hard biting, but still. I have tried saying “ow” loudly to scare her, made my hands go limp, hid my hands, got up and walked away from her, smacked her snout (not hard), put pressure on her teeth when my hand is in her mouth, and held her tongue down for a second. She pretty much just thinks I’m playing and is literally not phased. Anyone else have any other tricks? Thanks in Advance!

Photo is my girl Dixie!