"Derived from cannabis not hemp. Is this correct?"
Please keep in mind that hemp and cannabis are related, but they do offer different benefits. The doctor you spoke with may have made the suggestion based on your needs.
One major difference between cannabis-derived CBD and hemp-derived CBD is the extraction process. When CBD oil is extracted from cannabis, it's typically derived from the leaves and flowers of the plant, containing some THC. When CBD oil is extracted from hemp, it's made from hemp seeds or stalks of the plant, but it naturally never contains more than 0.3% THC.
Check out this article below that you may find helpful in breaking down the differences between CBD oil and Hemp Oil.
I hope this information helps! :-)