Am I being treated fairly on FMLA

I use FMLA for fibromyalgia. My limitations are such that sometimes I cannot work at all, other times I can work a few hours, etc. Three weeks ago, I went on FMLA leave to have breast reduction surgery due to fibromyalgia. I haven't been released from the doctor yet when this morning, 3 weeks later, I received a call from the human resource manager at this very large hospital/insurance company that I am employed with, stating that my FMLA has expired and I have been placed on medical leave. This means that when I am able to return to work, which was to be tomorrow, I have to check with her first to make sure I still have a job since I am not protected anymore by FMLA. My problem is they say FMLA is on a rolling 12 month period. I dont understand that because I first used FMLA a year ago in May. I thought after 12 months, in May, I would have the 12 weeks again but this isn't how 'they' do it. Please help me understand if they can treat me this way!!!!