Hi,
Sorry to hear that the advice has been lacking to date.
Please google 'piriformis syndrome' and see if it fits your symptoms.
I think that you may have a sciatic nerve tethered to the piriformis muscle, which is underneath the main buttock muscle. It is likely that you will have a tender point in the buttock, have difficulty striding out, be worse after rest or first thing in the morning as well as activity irritating the area if severely tethered. This occurs after having an inflammatory response and can happen some time after the initial problem (eg back pain)
Deep tissue massage, which hurts, is given over the piriformis muscle then gluteal and hamstring exercises are done afterwards for a few days. These exercises may aggravate symptoms if the deep tissue massage is not done first. The massage may cause bruising to the buttock. Scans will not show tethering in the buttock.
If you had a doppler ultrasound on the calf your lower limb blood flow should be ok - which would rule out the symptoms caused by poor blood flow eg intermittent claudication. If you wish you can provide feedback to me to clarify my thoughts. If what I am saying sounds correct I can explain a self treatment that may help.
Hope this helps,
MrPhysio+