Very tender nipples but not breasts?

I have always heard about tender breasts being a sign of pregnancy but never just tender nipples. I have currently an iud but my boyfriend and I don't use condoms ever. because of my iud i dont get my period at all anymore so im not really able to know if i missed a period. but the past month and a half i have been getting nauseous in the the mornings right when I wake up and it lasts for like an hour to 2 hours then goes away. but for the past week my nipples have been extremely tender to touch. and it is just the nipples not the whole breast. is that normal to be a sign of pregnancy or is it just the breasts.