i always have a period every 28 days. My boyfriend did pull out in time during sex and i was ovulating in july my period was late and when it came on it started out brown then when to red but it wasnt heavy like it usually is it lasted 4 days and was normal the last 2 days but when i came time for my aug. period i counted 28 days from my last period and i was late but when i can on it stated brown then it was brown and red and then it was bright red but it was really light and stayed that way for 3 days which is not normal for me when my period are alway heavy. i took a pregnancy test before my aug. period and i came out negative. could i still be pregnant