Long read, but help please

So I have read all of the descriptions about what implantation bleeding is. Light pinkish discharge that shows up when you wipe, only a little or can even last for a few days, etc.

I last had sex on June 28. I am on birth control and we used a condom. He didn’t come in me. My period was due to start on July 6 but instead of a normal period I got kinda what I described in the paragraph above. It lasted the normal length of my period but was still more dischargey then blood. I had been on antibiotics for about two weeks when we had sex and I got nervous and took a plan b.

When I started having the discharge instead of a normal period, I went and bought a pregnancy test. It came back negative. I had multiple sitting around and took one today and it was still negative. I think I am in the clear in saying that I’m not pregnant.

My next period is due to start August 8 and I’m really nervous that it might do the same. I only started birth control on May 26 so my body is still adjusting.

Could it be that a pregnancy test just isn’t working for me and I’m getting false negatives? I don’t have any symptoms besides headaches and every now and then weird cramps all over my stomach. The only thing I have done is fool around with my boyfriend some because I have scared myself. And I highly doubt there is anyway I could be pregnant from that...hopefully.

Or do you think maybe that’s just how my body reacted to all of the drugs and hormones in my body. I’m really anxious to see what my body does next week once my period is due to start.