You are on a high dose of hydroxyurea, which can have significant adverse effects. The sores on your ankles sound like vascular ulcerations. These are considered to be a very significant adverse effect and an indication for discontinuation of the HU. Note that this puts you at risk for gangrene.

"Discontinue hydroxyurea if cutaneous vasculitic toxicity (e.g., vasculitic ulcerations, gangrene) occurs in patients with myeloproliferative disorders; initiate alternative cytoreductive agents as clinically indicated." https://www.drugs.com/monograph/hydroxyurea.html

"Long-term treatment with hydroxyurea is associated with painful skin ulcers, aphthous ulcers, non-ulcerative toxicity with erythema, and skin infiltration.[17] Rarely, long-term therapy with hydroxyurea is associated with gangrene of the toes and digits.[18][19] The recommendation is to discontinue the drug." https://www.ncbi.nlm.nih.gov/books/NBK537209/#:....

Here is a bit more information.
https://www.epocrates.com/online/drugs/230/hydr...
https://medlineplus.gov/druginfo/meds/a682004.html

The good news is that there are other treatment options for MPNs that you may tolerate better. I was not able to tolerate HU. I have done much better on the interferons, Pegasys and Besremi. There are other options to consider as well.

Suggest an urgent call to your MPN care team is in order. If you are not already consulting a MPN Specialist, this would be a good time to do so.

HU is both a chemotherapy and a poison. These symptoms you describe are known side effects. Now that you have reached this saturation point it is doubtful any intervention other than discontinuing HU will help.

Speak with you physician about that and continuing on with another med such as Jakafi. Beginning Jakafi at a low dose and titrating slowly up should give relief plus control your counts. Jakafi has some anti inflammatory properties and should also relieve the discomfort. It will take at least a month or more for your skin to recover. Plan on gaining weight. Unavoidable with Jakafi.

I have been on HYDROX for the past 4 years. My dosage is 2-500 mg per day and 3-500 on Sunday. Sometime I do get a rash on my face I use a moisturizer everyday and that helps. You may want to ask your doctor it maybe time for a change in dosage or it could be something else all together.

Only you know best