He also replaces the nipple with his hands sometimes.
Could he be teething already? Gums look normal so far, but i can't think of what else would make a baby clench down this way.
It could be he is teething already. I was given really great advice that if you get a problem with a biter, pull them in super close as soon as they chomp down. It causes them to stop biting. Its worked!
Sounds normal. He wants to explore and look at stuff without letting go of his boob. My son did this and I had to start nursing him in dim rooms with NO ONE around to distract him. Even the hand thing is him probably just testing it all out. Mine was a phase that lasted a month or two.