I had chicken pox myself when Valentine was 2 months old. I was breastfeeding, and she had nothing!! Incubation time is of at least 10 days, so your baby was probably exposed already, before you even know it. I was worried too for Valentine due to her young age, but the doctor told me it would probably not but strong for her. And the time she develops the symptoms, I made enough antibodies, so she was fully protected! So, try not to worry too much
Doc told me she would protected perhaps for one year, not all life. Indeed, she had it at 2, at the daycare.
Afterwards, I was scared that I could have had it during pregnancy!...

I hope it's going smooth for your son.