4DPO what is this??

I know this is TMI but I'm currently 4DPO & been experiencing severe headaches for around a week now & occasionally itchy nipples, both are quite unusual for me. I went to the loo today as I started to feel abit of wetness & thought my period may have started as my cycles have been funny for the last 2 month, they've gone from being 5 days long to just 3, which is odd. When I went to the loo expecting my period, I got this instead. Anyone know what it could be??