Period Length Change

So since I can remember my periods have always been the same length  apart from last months which strangely lasted for only 3 days. The last few days I have been feeling extremely nauseous, veins in boobs have became extremely noticeable, nipples have gotten bigger & been an increase in aereolas on the nipple however they have not been sore. I have also been experiencing yellowish ewcm which I have never noticed happen before. I'm not entirely sure when I ovulated this month because i never used any opk kit as I decided to have a break from TTC. Any ideas what it could be??