When to stop

My hubby and I just had a conversation the other day of when do we stop not preventing getting pregnant (which really means when do I stop trying to get pregnant)? We have two boys, but I want a third and hubby is in the if it happens it happens camp. Coming Sept it will be a year. At what point do you just stop and accept that it wasn’t meant to be and move on? My youngest is 4 right now and goes into pre-k next year which means I go back to work. Ugh