<human>: My 18(almost19) month old nephew has been with me for almost 2 weeks now and he is horrible.

My sister was a drug addict, has 4 other kids who's fathers got them, but my nephews father is in prison, so I agreed to get him.

From what I saw, she was always on her phone, he had diaper rash all the time because she would not change his diaper until he leaked out, she never taught him anything, she hit him a lot for being bad, and his teeth are rotten.

So I start off trying to show him love, which he Is clearly uncomfortable with. Then I get on his level and talk to him why he cannot do something, and tell him no. Then he throws himself back when you tell him no, and he hits his head on the ground. 

If I tell him no, he will look at me to see if I'm serious and then he continues to do whatever I just said no to. Then I have to give him a time out, which makes him throw himself and cry.

I have a 5 month old who he has thrown things at when he's angry.

I don't know if I have to start hitting him as punishment instead of timeout, or if there is something else I should do. Help?

Can you summarize the given text in a few sentences?
<bot>: 18 month old throws himself back and hit head on ground when I say no; throws things, hurts himself, cries and will even gag himself. Should i spank him or keep timeout method? Help?