please help

I started my period on Sunday 29th January and had a normal period up until the Friday 3rd February, I had sex on the 3rd which was when it ended completely, I then had sex again on Sunday the 5th, anyway Tuesday the 7th I started to have some reddy/browny spotting then by the next day it was gone, I had sex again on Thursday 9th and once we were done my SO told me I was bleeding, I passed it off and thought he was just abit rough, anyway, I then proceeded to have another 5 day period but minus all the cramps I normally have with my period, what could be happening? In all the years I've been having periods this has never happened