This is easier said than done but
stop being frustrated. The puppy can sense your energy and bounces off that.
Don't be upset if you see poop or pee. He's already done it. He will know you're unhappy about the poop/pee but he won't know why and will just resort to hiding to pee/poop (he doesn't know you're mad about the ACT of him pooping, not the RESULT of him pooping. He thinks it's the latter.). If he is in the middle of peeing/pooping you can scold him and put him on the pad.
Something to keep in mind:
Once he learns that peeing/pooping where you don't want him to makes you upset, he will do it to spite you when he's upset. You've heard of dogs that get upset and LOOK AT THEIR OWNER while peeing right? They're doing it to push your buttons because they know it gets a reaction.
DO NOT let him have free run of the house.
Is the playpen small enough? It should just be his bed and his potty pad. Tape the edges of the potty pad down. Is his bedding washed THOROUGHLY? Is HE washed? If he is dragging the pee and poop smell everywhere, he is going to pee and poop on his bed because it smells like his potty area.
What I would do:
- Make the playpen small. Bed and potty. That's it. Put some toys in his bed so he has something to play with. He is playing with the potty pad because he is bored.
- Tape the potty pad down.
- This sounds gross, but the next time he poops or pees, pick/wipe it up and put some of the smell on the potty pad. Then it will smell like his "bathroom" and he will (hopefully) start to poop and pee there.
- When you come home, PLAY! He has been alone and cooped up ALL DAY. If you need to take him outside (so he can potty too), do so. If you can take him for a walk, do so.
- Discourage biting.
When he bites, say NO and put a chew toy in front of him. He is biting right now because that is how he plays, but once he's older it will be a big problem. Nip it in the bud right now. Some people like to do an exaggerated "OW!" and I've heard of some people faking crying. Or if he bites, simply stop playing, put him in the pen, and walk away. The puppy can pick up on this and will soon learn that biting is bad.
This link will be helpful for potty training:
Puppies at 3 to 3½ weeks - Time to start potty training
He will be the sweet loving dog of your dreams, but it takes
a lot of work. You have to be REALLY consistent with training.
A good helpful book is "Puppies for Dummies". I know some people hate Cesar Millan, but his book, "How to Raise the Perfect Puppy" is also very helpful.