If you might break through and ovulate, the pill also changes the chemical balance of the fluids in your womb that make it very hard for an egg 
(you; might break through; ) (you; ovulate; ) (the pill; changes; the chemical balance of the fluids in your womb that make it very hard for an egg; L:in your womb) (the chemical balance of the fluids; make; it very hard for an egg)
you you the pill the chemical balance of the fluids
might break through ovulate changes make
the chemical balance of the fluids in your womb that make it very hard for an egg L:in your womb
it very hard for an egg