Kel- I think if your totally "unlucky" I acually dont know if thats the right word.... then you might fall pregant. Im the same as you, Im not on contraception and we dtd all the time and although we use the withdrawal method there are some occasions where that first bit comes out before hes had the chance to pull out (sorry if tmi) and I havent fallen pregnant... but that could just be me!
If youre not fusses about having 4, then dont worry about it too much. GL