I've been doing it several times. Do you have to surrender or make him surrender? Currently, the only one who can my character pregnant is slime (Edit: it already works)
I know you already solved it, but for anyone else - this is usually caused by the pregnancy kink being turned off! In that case you can take the pill but it doesn't work (so it doesn't get used and you can't take another one either), but as soon as you turn the kink on you can get pregnant from the next creampie without taking a pill because the previous pill is still "loaded" for a lack of better word. Then if you turn the kink off while you are already pregnant, you still have to carry the pregnancy to term.