What Causes Burning Sensation In Nipples?

Hi...for the past 2 days i have noticed that my nipples are hurting...it feels like a burning sensation and its really bad especially wen i wake up in the morning and i feel like my boobs are on fire. My period came two weeks ago so am thinking that it couldnt be because of my period and i have had unprotected sex 3 weeks ago do you think that it could be because i am pregnant? please help me!!