I've Been Having Very Light Period Bleeding For The Last

I've been having very light period bleeding for the last three weeks? Normally my periods are shorter (3-5 days on average) and heavier. Most days so far it hasn't even felt like I've needed to wear any sort of hygienic pads but I still don't want to ruin any clothing. This started a week or so after I started new birth control. Is it just because of the new BC and is there a way to stop the bleeding?