No period after 2 years ???

I’ve had my IUD in since October 2016. I’ve missed my period this month and I haven’t done that even once after having my Mirena put in. I’ve been feeling nauseous a lot but I also apparently have an issue with the acid in my stomach as well which could be causing it. I’ve taken 2 pregnancy tests (both negative) in the last month, one two days ago and the other about 3 weeks ago. I am 9 days late. I could be pregnant but the possibility of that seem very low. Has anyone else had their period suddenly stop while using this?