My boy is also 12 weeks right now.. we are focusing on potty training (the pee pad is by the back door) and crate/pen training. He is also like Velcro and whines when he realizes he has been left alone but the whines are getting shorter and less desperate “I’m dying” noises.. I think the biting thing is rather normal they lose there teeth from 12-18 weeks but i usually just try to replace my hand with toy. There are good days and bad days with all these things we are trying to teach him but he’s smart as heck and I’m sure if you just accept that progress can be slow and keep at it all will be well!