6dpo slightly confused

Well by my reckoning I'm 6dpo today. When I woke up there was cramping pain (light not severe) in my left pelvic area. I did my bbt which had dropped a fair bit since yesterday and also when I did a cervix check my cervix had firmed up and dropped a bit. is this normal for this time of the month or am I getting my period early?? As it's not due for another 8 days