4days late

I'm 4 days late, my last 2 periods started 3 days early, I ovulated normal. I told my SO and he says there's no way I'm pregnant. I told him he needs to go buy me a stick to pee on and he's going to today. It hurts when we have sex and it shouldn't cuz my SO has a very less than average unit. My 14mth old is still breastfeeding. So another baby wouldn't be ideal, but every baby is a blessing. How much harder can a 4th kid be?