Weird period...

So. I hadn’t had a period in five months since I got the depo shot. Stopped working in September. Say I had unprotected sex (came in me) two weeks ago. exactly six days after it happened I got a very light brown discharge. Didn’t need a pad or anything since I only had it show when I wiped after going to the loo. I had light cramps. Lasted six-ish days. Could it be a sign or just messed up from BC?