What Causes Delayed Periods With Enlarged Glands Behind The Ears And Nausea?

I have a late period, last Jan. 22, 2011. Change in vision, headaches, and very tired. I also, have two enlarged glands under my ear that are swollen. What is going on? I am not pregnant. I am 30 years old in good health, walk daily for 3-miles, have three healthy kids. Please help me. It is very difficult to teach my 1st grade classroom.