My dog bit me when he was in pain?

to join us, Jhonalid1!
I believe your puppy bit you out of fear and pain. If you were bleeding, I would be more worried about yourself for the moment. Perhaps take a shot for the precaution?

Since your puppy usually just "playing biting", it is not too much of a concern, although in my opinion you should avoid putting your hand near its mouth. It is indeed a bad habit of your puppy which need to be corrected.

I am not a dog expert, so I will let the more experienced dog expert members to answer the details.