No period for over a month now....

So my fiance' and I started TTC almost 5 months ago. So far no luck. We were preggers in 2014, but then I got really sick and had to go into hospital. I was diagnosed with Type 2 Diabetes and they found tumors in my uterus. They had to abort our baby to save me. But I kept my uterus & was told I could have more children. Anyway, my period had been pretty regular since that operation until this month. I haven't had a period in over a month. But I took a couple of pregnancy tests & all come back negative. Any ideas?