I ovulated on the 10th and had unprotected sex on the 19. I started my period on the normal date (feb. 23) but my flow has been heavy ever since I got it for the first time at age 10 and I'm 17. But this time it's really light. Like I one pad would do it for a whole day kind of light when I usually would have to change 4 to 5 times a day. Is this change normal from time to time or could I be pregnant?