Birth control pills are hormonal pills that help control timing of pregnancies and prevent unintended pregnancies. There are many, many different forms and pills, but they all generally work in the same fashion - they work by suppression of ovulation, thickening cervical mucus, and endometrial changes that interfere with transport of sperm to egg and with implantation. Unfortunately, it is common to get breakthrough bleeding in the first 3 months especially if the pills are not taken consistently at the same time daily. If you continue to bleed or stain, you will need to see your gp to get a different pill. However, regardless, you should see your gp 2-3 months after initiating birth control to assess tolerance, as well as blood pressure. Abdominal pain, nausea, bloating, headaches are all common side effects with birth controls.