Can Nerve Root Block L4 L5 And S1 Cause Severe Migraines?

I had a nerve root block, L4 L5 and S1, Dec 11, 2009. Ever since the nerve root block I have had migraine headaches, every day! I never had headaches before. I have had 4 blood patches and it doesn't look like I have a spinal fluid leak. What would be the reasons why I have had such horrible migraines since by nerve root block?