No period in 2 months? Started birth control 2 weeks ago

Hey guys,

So I took Plan B after a condom broke (and I wasn't on birth control) on May 22nd and had a normal period May 31-June 4.

Then, I decided to get on birth control so this doesn't happen again. Per the instructions, I was waiting until I got my next period to start. Around July 15, I got what I thought was the start of my period. I had a bit of cramping and some light brown spotting, so I thought it was starting. So, I started the pill that day. Then, it completely stopped.

So, I basically haven't had my period since May 31. I took a few pregnancy tests a week ago and they all said negative.

What could be going on?? Any insight? Thank you!