Nipples sore on progestin only BC

Hello! So I started taking progestin only BC and am on my 5th week. I've had just spotting and no other symptoms however my nipples started getting tender yesterday. Nothing else just a slight tenderness. I really don't think I'm prego, but wondered if it's normal. SO hasn't came in me since I started BC, we've been using condoms and the pull out method. I've also been taking the pill at the same time everyday (within 15 minutes of my scheduled time). Should I be worried at all?