Can muscle cramping be a side effect of taking hydroxyurea?

Not commonly: It's not a common symptom of Hydroxyurea but Hydroxyurea can cause nausea, vomiting, diarrhea and renal impairment which can cause muscle cramps. Not sure you have the above symptoms.

Not likely, possible: While nausea, vomiting, diarrhea, and flu-like symptoms are side effects of hydroxyurea, muscle cramping is not a *directly*. However, other side effects may indirectly cause cramping. Have you had vomiting/diarrhea - dehydration may cause cramps. Also, the drug’s been associated with drops in magnesium levels, whose symptoms include muscle cramping.