Period Talk: What’s going on? HELP!

So my periods have always been irregular. It’s normal for me to skip a month or 2. Long story short, I had gotten my period at the end of August, skipped September, then got it again at the end of October. My cycle lasted 5 days. Well, 10 days after the end of my cycle I started bleeding again, but this time it only lasted for 2 days. Now I have uncomfortable cramping and a brownish discharge.

Prior to the 2-day period I had unprotected sex a week before.

Any idea on what could be going on? I haven’t had this happen before.