I Had Sex In August, 2016. We Used A Condom

i had sex in august, 2016. we used a condom and i have not missed a period since. however, my last two periods have been very light; almost nonexistent. i am on birth control and have been since about june 2016. sometimes my stomach churns but i havent had any pregnancy symptoms. i took 2 pregnancy tests, one 4 weeks after, and one 5 weeks after. thy both came back negative. is it possible i am pregnant?