No period since IUD removal?

I had an IUD (Skyla) inserted in August 2015, and removed in December 2015 due to negative side effects. Since having it removed I have only had one really light period in mid February. 
I have changed my diet and exercise routine dramatically, but that's all I can think of that would contribute to what's going on. I've taken several pregnancy tests since then, and they have all been negative.  I took them just in case, but we use condoms every time. 
Does anyone have any ideas what could be going on, or experience with this?