Confused.

My tubes have been tied since November 30th 2017 my periods have been normal for the most part give or take a day or 2 which is unusual usually I have no problems I some times have gotten faint lines on any test you can but 3 months after my periods keep coming so I'm not worried but yesturday was the start of my period or supposed to be I had spotting all day today and yesturday I had what felt like contractions in my back I went to bed and woke up and am I am still spotting I took a test yesturday and it showed something faint before the test even finished running now I am confused has this happened to anyone else before I thought u can't get pregnant that's what I got my tubes tied for do I go to the doctors idk what to do any advice ladies