As a mother, do I have the right to know where my sons father is taking him on overnight stays? My son is an infant.

No, unless the visitation order says he has to tell you.

Legally I think not. Sucks! But in my opinion... I believe you should know... it is your baby! I know how uncomfortable this situation is, but usually it isn't as bad as we think it is! Just ask the Dad where he is going. Don't be demanding... just ask.