Telling Coworkers Your Pregnant

Arwen
I just found out yesterday that I'm pregnant. I'm only 3 weeks 6 days. This is my fourth child. My husband and I always wanted a large family. At school today a coworker said that I looked really pale and asked if I was pregnant again. I said no. She said she knew that I wanted more and that I didn't look well. I felt totally fine. The only person that knows is my husband. I think when the time comes I'll say I didn't know that I was. Has anyone guessed that you're pregnant and what did you say?