Not immune to Varicella

So, as it turns out, I am not immune to Varicella. I keep questioning how in the world this has happened, as you would think I would have been vaccinated as a child (or at least I thought) for school records? I have lived in and went to school in Colorado my entire life, aside from a few months that I spent in NM. I’m currently 8w1d with baby #3. I remember specifically being told I wasn’t immune with baby #1, but I don’t remember anything ever coming up after that pregnancy or if I took a vaccine for it after either of my previous births. Is it possible I have been vaccinated and never developed antibodies to the virus??? I’m so confused at how I was not vaccinated as a child, considering my mom was always on top of that stuff, and how I could be so negligent as to not then be vaccinated as an adult??? I never had chicken pox as a child.