What Causes A Light Menstrual Period?

I had sex with my husband on july 8 until now..pretty much every day...and im on birth control..but i took amoxicillin on the 8th...i took it for 4 days..i was wondering if i could be pregnant. my period was only a couple days late. im bleeding now but its really really light, and its never been like this. Im just wondering if i could be pregnant?..a lot of people are telling me that its too soon to know and that I should wait until my next period....i just really hope that im pregnant..