If you have been taking your birth control
pills regularly without missing any doses, then the likelihood that you are pregnant or experiencing a miscarriage is quite low. However, anytime you have symptoms like this, it is important to see your regular primary care doctor
or OB GYN doctor. As part of the work up they do, they will most likely perform a pregnancy test which should sort out that question for you.
Another possibility is that you are experiencing break through bleeding
. This is relatively common in people taking birth control pills, especially if you have been on them for a while. Basically what happens is that the birth control pills lead to gradual thinning out of the uterine lining. This thin uterine lining is very fragile and, occasionally, small blood vessels under the lining might become irritated and burst open, leading to light bleeding. Typically this occurs about half way through the pack of birth control pills.
Your doctor will be able to perform an examination and confirm whether or not this is break through bleeding. If it is, solving the problem will sometimes require switching to a different form of birth control, and your doctor can give you advice about this.