Can my employer fire me 3 days after finding out that I am diabetic?

I have worked at my job for 4 years and 10months. In that time I was written up only once for a disgreement with another employee. That was two and a half years after I started. I have had no other issues at my job. On May 2nd,I found out that I was diabetic. On Tuesday, my supervisor asked what the doctor had said, and I told him. On Friday, May 6th, I was fired for miscounting a skid of candy. I was told that they did not think I could handle the way that the company was moving. I was then asked to leave the property. Also, a year ago, my daughter was diagnosed with Rett's syndrome variant, and Autism spectrum disorder. She has been recieving ABA therapy since Sept. 2010. I am the one who carries the insurance for my family.