My period has always been normal I had my last normal period on April 14 and the other two after that has been dark brown blood and only last 3 to 31/2 days where they usually last 5 to 6 days. I have taken 2 pregnancy test and they were negative. Unprotected sex on April 19, May 9, and May 18. I am not on any type of birth control. Should I go and get checked?