Partner wants sex

Tia
Im 20 weeks with my second and every day my partner will ask and ask and ask if where having sex later on and I literally have nothing in me, I dont want to and I have no interest at all, he gets shitty and I think he goes and does hes own thing by him self, but I cant help it , I try to for him but it hurts aswel, and my tummy feels weird during plus my one year old runs me tired, aah anyone else