Hmm - want to switch games? =P I am playing two challenges at the moment and so far, only one of them has hit the 'baby stages' (the other one is the Legacy one and I just started a bit ago. :x) and both times I've had one baby. the surprise was. both pregnancies were girls. I have been having all boys in my other saves, so I was like... squealing excited, lol.
On a more serious note - sorry to hear that you're having some difficulties with your game. It kind of sounds like that one bug where at the beginning some Players were constantly just having multiples, but that was earlier when Sims 4 just released; and a few of us didn't experience it, though. but like Rose said, it could be that your mod is out of date and that's why it's no longer stopping the multiples.