Our concerns from HCM. The posterior headache that you describe with position change is probably due to cervical spondylopathy as nerves to that area arise from the neck. I assume that you are on calcium supplements in view of renal disease. Now for pain relief I suggest hot fomentation to the neck and also taking pacetomol 650mg(safe to kidney) when it pains a lot to a maximum of 4 times a day. Al I also suggest X-ray of cervical spine and review.