I get horrible migraines whenever i donate blood or have it drawn. i always make sure to eat before and after and drink water. could this mean anythin?

All has meaning: Strong negative physical reactions to blood loss of even small amounts are most likely to be mainly emotional - but to medium or large amounts the physical causes increase dramatically. It's good that you prepare as you do and you've selected good things. If you have no other issues - just try to bear it as you do, and avoid it if optional. Phobia Tx is not needed unless there are other ones too.

Mind over body: If even a small lab draw can trigger you, then it is not something like volume depletion...it is your eyes, or pain response, or thought process that is likely triggering a physiologic response (aka: stress or "fight/flight") and those hormones are contributing to triggering your migraine. Should talk to your Dr and consider positive imagery / biofeedback / similar PREEMPTIVELY to minimize/stop.