I woke up the past two nights in a row due to my nipples being extremely hard and felt like they were burning, nothing helped ease the pain but I became so tired I finally fell asleep and woke up hours later with no pain. I am not pregnant or ovulating. I am expecting af in one week. Does anyone know what is causing this to happen? I searched online and only found this pain associated with breastfeeding which is not the case with me.