You need to know that Sibelium has role only as a prophylactic agent. It means that it reduces the frequency of your headache. It's not meant for Acute treatment of migraine.
Next Steps
Consult a neurologist. First of all diagnosis needs to be established. All headaches are not migraine.
If it's migraine then treatment includes a medicine for acute relief of pain with or without a prophylactic medicine (depending on frequency, severity).
Health Tips
Each medicine has its own risk benefit profile. Medicines can be prescribed only after knowing into the depth of your problem and any other comorbidities.