Isaac's dilemma

So i killed Mom in Isaac and soon had to play again to kill the real last boss in the game. Strangely after killing mom it only took me a few tries to get 2 levels further and kill the last boss. Not only did i kill the last boss, but i killed it with 3 different characters in only a matter of a few tries. Now with playing Isaac i just don't manage to get to the last boss again. I tried about 10 times now and i just die and that pretty early on. Often i die at mom, although she isn't really hard to beat at all. I think i may just have to get a bit better. At least the game isn't getting to easy for me, nor boring x)