Why Might I Have A Reddish Brown (old Blood Colored)

Why might I have a reddish brown (old blood colored) discharge over a month after my tubal ligation? Before the tubal, I was on the pill and hadn't had a period for almost a year. After the surgery I had two periods which only lasted about 5 days. I just chalked it up as my period was regulating from being absent for the better part of a year. Now I just have random spotting and discharge, not necessarily at the same time.