According to your history there are different issues troubling you. The most common cause for painful knees will be osteoarthritis
which is very common after 40 yrs of age. The swollen vein is called a varicose vein
which is commonly seen in ppl engaged in activities which require prolonged standing but again this has nothing to do with the knee pain
. The other pain that you are complaining about the butt cheek and the leg pain can occur either because of a vascular obstruction or because of a neurological compression in your back. I would suggest you meet a general surgeon
or an orthopaedic surgeon
who will be able to guide you better.