We can't say for certain what the cramping is, although given the timing it sounds like it's related to your withdrawal bleed (the period you get on the pill). Can you clarify for me if the pill you, "missed the night before" was taken more than 12 hours later than it's normal time? And how are you feeling about using the pill as a method in general?
Too, since it sounds like you do not wish to become pregnant right now, a great way to lower any future risks is to combine your pill with a condom. Do you feel comfortable asking your partner to use a condom going forward?