On the 4th of November, I had unprotected sex with my partner. Because it was on a Friday, I didn't have access to the morning after pill until Monday morning, which was cutting kind of close. I experienced nausea and cramping, normal side effects within the first 2 hours of taking the pill. Then, on the 20th I had on and off cramping with some spotting. The spotting was brown. It continued like this for about almost 3 days until I got a moderate/heavy period that included fresh and brown discharge. It was a lot less intense than how it usually is (I have dysmenorrhea). Oddly, the pain I got from the spotting got worse when I walked anywhere or ate something, also true when It got heavier. Is this normal? Should I be concerned?

It is likely from the morning after pill which can disrupt your normal cycle due to the higher concentration of hormones. See what happens when you would expect your period for December.

The morning after pill is of course not 100 percent effective even when taken on time. It is not a matter of making it on time, it is a issue that the longer you wait, the less effective it is.

It will alter your period for one or two months but if you have concern, a trip to your doctor is never a wrong thing.
Most likely it should be getting cleared up by next period.