What Causes Production Of Milk After Stopping Breast Feeding?

I stopped breastfeeding five months ago. It took a little over two weeks for my breasts to stop producing milk. In the last month I have began to produce milk again for some reason. I also have had other symptoms of pregnancy. I went into the doctor and he did a urine pregnancy test and it came up negative. What could be causing the milk production and other symptoms (ie no periods for 3 months just light spotting, weight gain, morning sickness)?