Lactating after 6-8 months cessation

Hey all!

My LO will be 3 next month. I stopped pumping when he was 2 months old and weaned him to formula. About 6-8 months ago I stopped being able to self express breast milk. Last week it started again once I hit my fertile days. Period is due in 5 days according to glow. Anyone have this happen? Should I test for pregnancy now or wait?

We are not actively TTC as I am finishing up nursing school. I have a mirena IUD that won't be coming out until I graduate in may.

Thanks ladies!