Use of Pain Killers for long time itself can cause headache. Though it is sometimes helpful to get medications over the counter, they are counterproductive most times.
Your headache may be because of stress/tension, handling it the right way will save you from medications. But, There are many other reasons for headache - Sinusitis, Migraine etc.
Next Steps
Meet a Physician or a neurologist.
Health Tips
Stop self medicating.