Hydrea (or generic hydroxyurea, sometimes people here abbreviate it to HU) is an oral chemo pill that reduces platelet count. If you have essential thrombocytosis (ET), it can prevent complications from too many platelets. Most people tolerate it pretty well.

I am so sorry to hear you are in pain. That's not common in ET, though clots or circulatory problems associated with ET can be painful.

I am not clear from your post or profile if you have ET, but I hope you can get to the bottom of things soon!