Have I had chickenpox before?

I'm 16 and I thought I'd never had them before. But my mum told me yesterday that she remembers me having lots of spots on my body when i was about 5, and a fever, and she rung up the doctor and they said it sounded like chickenpox, but the next day the spots went :S Also, she put me with children who had chickenpox, and I never showed symptoms, but I went to a health advisor and they said I've probably already had them if I have been with children who had them, however a very mild case, I never knew that could be possible?