My new chihuahua puppy that i got like 5 weeks ago always bites and scratches me!!!

I tell her "NO Belle!!" but she doesn't care, she just keeps on biting.

One time, she bit me so hard on my index finger that she cut it open!!!!

I know!!! I have scratch marks now and when I go somewhere, I have to wear a sweater to cover my scratches!!.

What do I do!!!