My cockatiel won't stop hissing at me?

Hi, about 1 week ago I got my very first cockatiel (I've had other birds before) I gave him some time to settle in and after that i was able to pet him slightly and hand feed him treats and get him out on my finger and on my head, he's only 10 weeks old BTW. Now he just won't stop hissing at me and biting me I haven't been aggressive or done anything to scare him, I do personally think I've been careful around his cage. What do I do? Is it normal?