smoke the weed by it'sself, if you still get it, it's some how related to the weed...

did you have even the slightest headache (possibly even drank the night before but didn't have the hangover head ache yet) or were you coughing your ass off?

holding in the weed smoke seems to increase my blood pressure (i guess? lol, i dunno how to explain it, close off your throat and blow as hard as you can, you know where it feel slike your face is slow expanding from pressure) greatly, and can take even the slightest headache, even one that i don't really notice, to full blown throbbing... even if it's good weed...

but if none of hte above applies and you smoke it by it's self nad still get the headache, it's just the bud quality..