Getting asked when are you going to have another child?

Tina • Married my best friend. & we have our son 5yrs old. Ttc baby #2.
I get asked a lot when I'm going to have another child. My husband & I have been Ttc for 4 yrs. My son is 5yrs old. I have hypothyroidism & pcos. It's hard for me to answer ppl when I'm asked. (So when are you going to give your son a sibling) I try to stay positive & hope that one day I'll be blessed w/another child. 
I just don't know how to answer ppl. What are something's you tell ppl that question you about having more children?? Or how do you deal with the question when asked??