So I'm currently a little late on my period but my cycle is very irregular or (previously, as of 5 months ago) nonexistent due to the mirena IUD. I took a pregnancy test today, 16 days after I last had sex, and it was negative. I've said this on here before but my partner and I also use condoms very carefully every time we do anything. My question is that even with a missing period, my breasts are pretty swollen and a little tender. This is something I get often before my period, but since I'm late I'm not sure if this period related or not. What else could cause swollen breasts? I took the test correctly and was careful about taking it first thing in the morning too.