I've been on the implanon for about 2 years. I went the 1 year without my period. After a years I started getting normal periods every 27/28 days lasting for about a week. Last period was a week ago, I was on Amoxicillin. Right after my period was over I had sex and he ejaculated outside of me, because of the antibiotic, which makes birth control methods less effective. Now 4 days after having sex I got my period again. Is it normal? Am I pregnant?