Are you on the pill? When did you start that?
Are you using any other medicines?
How old are you?
When did the spotting start?
How long has it been going on?
What is your cycles like?
Are you sexually active? Are you STD free?
What does your mucus cycle look like? Do you have itching, burning or a nasty smell?
If there are no obvious medical reasons for it, birth control pills will often be used to stop spotting. Sometimes an NSAID pain killer (like Ibprofin) can be used to thicken your blood a bit. Do however make sure you read and heed the warnings if you try that.