Verapamil Hydrochloride and migrane

I am a long term sufferer of migranes and take daily tryptans to control them. My physician put me on verapamil for high blood pressure and for a year or so I was comfortable with the regimin. However, now when I take the verapamil I develop a staggering headache within an hour of the dose and am at a loss? I have experimented and not taken the drug and not had the headache and then taken the pill the next day and the result was a migrane that came on in spite of taking the tryptan....axert. Is there a reason for this happening?