I quit birth control in jan, took 4 pills in apr, then quit again. had period 12 days later, but have now skipped 2 periods. why? (3 neg. preg tests)

Irregular periods: If you have been having sex, you might be pregnant. Irregular periods are very common, and that could be what you're experiencing. If you think you might be pregnant, I recommend you do a pregnancy test after another week or so.

Post pill amenorrhea: It is not uncommon to have skipped period after taking birth control pills for long time. as long as a sensitive pregnancy test is negative. I would recommend you protect yourself by other contraceptive methods so you don't have to keep worrying about pregnancy until normal periods start spontaneously.