Hi @jola13 Headaches are so miserable and it sounds like you have a doozy. I looked for other members who are taking HU and it looks like a headache with hydroxyurea can be common side effect.
Here’s the conversation with members @eileen11108. @ontheverge @sand103 @sregiani who’ve experience headaches while on HU.

~JAK2 V617F Essential Thrombocythemia: Hydroxyurea causes headaches
https://connect.mayoclinic.org/discussion/jak2-v617f-essential-thrombocythemia-hydroxyurea-causes-headaches/
Other possible relevant discussions where you might find some useful tidbits such as asking your doctor to reduce your dosage. That seems to be the theme when patients are having aggravating and ongoing side effects.

~People living with ET and taking Hydrea: Anybody setting
https://connect.mayoclinic.org/discussion/anybody-setting-records/
Actually in this discussion group that you’re currently in, this comment was made last week by @eileen11108 about her headaches with HU and the change in doses until her doctor found a balance.
https://connect.mayoclinic.org/comment/892038/
I know reading is probably the last thing you feel like doing right now but I hope these help. If you haven’t, please call your hematologist and talk to them about your headaches. You don’t have to endure those when changes can be made.