It depends a lot whether he was an identical twin or not.
If so, it's just a chance that the egg split, if he was a fraternal twin(non identical) then it is a hereditry thing.
However,the thing to look for is if the history is on your mother's side of the family such as your mother or grandmother was a twin etc...
This certainly increases your chances of a multiple birth.
Also if you are over 35, each subsequent pregnancy and you have conceived twins before.
however, this doesn't all guarantee a multiple birth.
I have twins and had a failed pg last time with twins but this time I am (happily
) having one, I'm going for the easy life this time!
Twins are a joy and I wouldn't be without them double the love makes double the work so worth it.
Also worse symptoms do not necesarilly point towards a multiple birth as i felt a lot worse this time than my previous multiple pregnancies!
Good luck with however many you may have x