What Could Short Periods Followed By Having Unprotected Sex And Brown Discharge Indicate?

Hi Doctor Grief,
I had my regular period on January 7 and it lasted until the 12th.

Then I had unprotected sex on January 17th. But he pulled out really, and I took plan b an hour later.

A week later, on January 23rd, I got my period again which was really weird considering I just had it. I know plan b does weird things like that though such as making it come sooner. It lasted until January 26th, which was shorter than my regular period.

I had unprotected sex again on January 29. He pulled out again really early, and I didn't take plan b.

4 days later, which was yesterday, I had brown discharge. It's still happening today too. Its not a lot. And it definitely doesn't look bloody. Its just brown.

What could this mean? I know theres always a chance of pregnancy but I really doubt it. Is this just plan b hormonal affects? Or maybe a cleaning out of my last period since it was short? I'm very confused.

Please help!