Sensitive nipples

Okay so I've never had this before and it is worrying me! My nipples are like crazy sensitive they just started maybe close to a week ago. I don't wear tight stuff at all so I know it isn't that. But boobs will go into terrible pain but my nipples hurt and are sensitive 24/7. My period is supposed to start the 16th and I've taken test and they all say negative... does anyone know why my nipples are so sensitive could I be pregnant and the test not picking it up yet?