I had a period 16 days ago, since then I've had really sore and uncomfortable boob's- which I usually only get for a few days prior but this has been for around 10 days. Today I've come on again randomly! There's no possibility of pregnancy so it's nothing to do with that. I've also had all my bloods checked recently, including my thyroid (I'm underactive), all is fine except low B12. Could this just be a one off random thing or should I be concerned? It's never happened before. I'm not on the pill or anything, which I know can cause it. The only stress I really have is just from being very tired from the B12...just very strange and annoying!