If you lose a monophasic COMBINATION pill:
Call your doctor and ask for a replacement pack asap. If you lose an active pill, take the next active pill in the pack asap
If you lose a placebo pill, it's fine to skip the dose as those pill do not contain any hormones
If you lose a pill and fewer than 48 hours have passed since you took your last pill, the CDC recommends taking the skipped dose asap, continuing to take a pill at the regular time of day (even if it involves taking 2 pills in 1 day), and consider using emergency contraception (morning after pill) if pills were also lost or skipped in the last week of the previous cycle or earlier in the current cycle. Returning to a reliable dosage of birth control becomes more difficult if you have missed 2 or more doses, or it has been longer than 48 hrs since the last dose. If this is the case, you should take the skipped dose or doses asap. You should continue taking a new pill at the regular time, even if it means taking more than 1 pill in a day. Use an additional form of contraception for the next 7 days, until a week of regular doses has passed. Consider using emergency contraception (morning after pill) if you have had sex in the past 5 days and the missed dose or doses were in the 1st week of the cycle.
If using a 28-day pack and the missed doses took place on days 15 - 21 of the cycle, skip the hormone-free doses and start a new pack right away. Use additional methods of contraception until you have taken doses that contain hormones for 7 days
If you lose a PROGESTIN-ONLY pill:
If you miss your 3-hr window and it has been 27 hours or more since your last dose, CDC recommends taking the next dose asap, returning to a regular dosage schedule (even if it means taking 2 pills in a day), using additional methods of contraception for 48 hrs, until you have taken the pill regularly for at least 2 days, and considering using emergency contraception if you have had sex before 2 days of regular doses have passed