Had little bleeding on the 13th of this month i quit my birth control a week ago ni had sex feb 1 i was still on birth control pills now i am bleeding took a pregnancy test it came out negative what could it be ?

BC & bleeding: BC pills are hormones so if you will stop the pills you may start bleeding ( just like when you are on placebo pills). https://www.healthline.com/health/stopping-birth-control-mid-pack#how-birth-control-pills-work Dont worry. But in any event since even BC pills are not 100% effective would repeat pregnancy test in 1-2 weeks though most likely just due to stopping pills.