Any pain in the pelvic area is hard to diagnose because it is such a large and complex area. If you look at my previous post/page on the pelvic floor, the diagrams there show just some structures that the pelvis contains. As mentioned before, it is apparent that the coccyx can be affected by problems from other structures inside the pelvis. So while you may purely and simply have coccydynia through an injury or degeneration of your coccyx, it may also be compounded by other things.
With pelvic varices, as with varicose veins in the legs- the valves in the veins become weakened, and their ability to pump blood back up to the heart (working against gravity) is affected. This means blood can 'pool' and veins become swollen, distended and 'congested'. This is because of the resulting backflow, or insufficient flow of blood.
As with coccydynia it is surprisingly hard to diagnose, and for many women goes undetected. Ones bladder and bowels can be 'irritated' and the pelvic area can ache- it may be a dull, dragging ache, or a sharp, stabbing pain. It can cause menstrual problems, and painful sexual intercourse. Sometimes varicose veins are visible externally. These symptoms and signs are why it is known as a 'syndrome'. I have looked on Facebooks 'Pelvic Congestion Support' page- and the amount of women (and men) who say it causes coccyx and lower back pain is surprising. Sufferers also complain of buttock, rectal and leg pain.
For some coccydynia sufferers this could be because these dilated veins are then pressing on other structures within the pelvis, which in turn press on the coccyx or nerves, muscles, and ligaments supporting or supplying that area.
I am not advertising the Whitely Clinic, but it has the best explanation of this condition that I could find. This diagram clearly shows how dilated blood vessels near the coccyx may cause or worsen coccydynia.
What is again obvious is that coccydynia is far from straight forward. It has a myriad of potential causes, and therefore diagnosis is made harder, and getting the correct treatment harder still.