Not related to cancer, but maybe your cramping and the hydrochlorothiazide (HCTZ) are related. I used to be on that drug and couldn't keep my electrolytes near the normal range, particularly potassium.

Low electrolytes can cause cramping. A few years before I was diagnosed with cancer, I changed cardiologists and the new one took me off HCTZ and put me on Spironolactone which is potassium-sparing. Goodbye low potassium.

Your medical team would have to weigh in on the wisdom of changing meds during chemo, but in the meantime you can try an electrolyte boosting drink with your medical team's approval. I do Gatorade G2 or Gatorade Zero when I have cramping - others use Pedialyte.