Sex when pregnant

We are having our first baby in Feb 2017, so happy/excited!  So I'm 17 weeks pregnant. In these 17 weeks we've had sex once. My husband is getting frustrated. I just have no desire for sex! Does it come back again? Any advice? I worry it won't come back even after giving birth as I'll be so exhausted looking after our baby. How do other expectant mothers deal with this? Xx