I think my puppy thinks I’m a joke

I think my puppy doesn’t respect me. I have him for almost 3 weeks and I was trying to train him by positive methods and don’t physically punish him. But now, I’m feeling like he thinks he can do anything to me and I will let it slide.

He bites on walks, like really hard, I have bruises on my legs and bite marks, he aims for the back of the knees and thats especially painful. I usually trying to distract him by some command, usually ,,sit” and it works for few seconds, but then he is at it again.

He humps me, just me, he never humped anyone or anything else. I don’t know what that means or why does he do that. At first I thought he just does it when he is excited, but now it doesn’t seem like that and he is starting to do it more and more often.

And lastly, he barks and growls into my face. Not just the playful barks and growls, it seams like he ,,talks back” to me. Usually he does that when I tell him to not do something or to stop doing something.

I don’t know to ho resolve his behaviour without physical punishments, and I’m desperate, as I feel like he hates me or that he doesn’t respect me.