I started birth control this month. i had bleeding the week before placebos for 4 days. only red 1 day. no period on placebo week. common or pregnant?

Common: Pregnancy can happen on birth control pills, but uncommonly. Get a pregnancy test - if negative, keep taking the pills as directed. Sometimes it takes the body a few months to adapt to birth control pills.

Not unusual: Particularly if this is your first month on the pill, it's not uncommon for your period to be a little off. That said, a pregnancy test wouldn't be a bad idea either, just to be sure you aren't pregnant.