Yes, My 12 Year Old Son Has Been On Vitamin

Yes, my 12 year old son has been on Vitamin D3 2000 Unit SFGt for a few years now because he suffers from severe leg cramps. December 27th I had his prescription refilled. He takes a pill a day. He started experiencing really severe cramps in his legs, arms, and feet. I have used CVS for years thus tryusting them whole heartedly until his condition continued to worsen. I looked at the bottle and he had been given someone elses prescription. This persons prescription is Vit D2 1.25 Mg (50. __000 Unit) and is taken once a week. I am so scared because of elevated cramps. Is there a need to be concerned?