pregnant but had tubes tied?

I had my tubes tied about 19 months ago. I've got two kids, and had pretty regular periods even while breastfeeding. I was supposed to start 8 days ago, and on the day I was supposed to start I spotted when I wiped and was cramping, but then never actually started. A few other days of cramping but no period yet, and I'm constipated. Any thoughts? I wanna take a test but not sure if I'm just over thinking this?? Anyone else have any experience in this?