A tough situation. Yes memory loss is one (of many) possible side effects of morphine use. Prescription drug use is often a tradeoff between two less than optimal situations - the original problem and the side effects from attempting to fix the problem. Ultimately you may have to decide which is the better alternative; increased problems with pain or memory loss.
I have read that while morphine is usually the drug of choice for pain pumps that other drugs can be used. Have you inquired about them?
Good luck!