the doctor appears to want to help you. take him up on his offer to redo the letter including other medical issues you have that he doesnt see you for and forward it. because he has already sent a letter on other medical issues does not preclude him sending another letter on additional issues.
usually the doctors only write about the medical issues that they treat. if you have other doctors for your additional medical issues you should try to have those doctors address in a letter the issues that they treat in their specialty.
social security will give greater weight to the opinion of a doctor in the specialty for which they are treating you.