I don't understand 😔

I've been ttc for three months now. I'm due to get AF in two days. I took a first response ept and it was negative. I have two boys and with them I wasn't even trying and was instantly pregnant. I've been following when it says my fertile window is but I'm feeling upset because I know the hubby doesn't want too much time between the ages in our kids and I feel like our window is closing. Any advice?