Why do you get a headache after crying?

Headache and crying. It may be due to the emotional stress that caused the crying or it may be related to the muscle contractions that occur as you cry. I would suspect it to be benign especially if it doesn't happen all the time or is mild. Good luck.
Usually, the opposit. Crying is often a release of stress, that stems from a meaningful loss (friend, spouse, loss of good health, etc), an experience that wells up emotion (like a good movie): usually this is a kind of 'letting go' response, which is healthy. Distinct from one that cries very frequently and is not an emotional release, or cries for secondary gain, with purpose of getting someone's sympathy. Check c gp.
Probably... ...Because of the stressor that got you crying in the first place is still there after you are done crying.