Unusual pain in thigh, front and back, back of knee and mostly back of shin.

You do not give your age or presence of other medical problems. If you have these symptoms when you walk, I am very concerned about Peripheral Vascular Disease (narrowing or clotting off of Arteries to the leg. Other things that can cause this are Chronic Dissection of an Aortic Aneurysm.
I guess this could perhaps also be a Deep Venous Thrombosis, but I would expect more constant pain and perhaps swell of the lower leg.

Your doctor can order an Ultrasound of the Blood vessels of you abdomen and legs to rule these out...

I am 40 years old. I am in; well lets say not good health. I have Reflex Sympathetic Dystrophy Syndrome in my left arm and left leg. I also have Pancreatitus, GERD and Irritable Bowel Syndrome. I have had numerous EGD's and colonoscopies because I stay sick most of the time. They did a food movement study and after the 4 step test was completed, I still had 100% of my food still in my stomach. I have had my gallbladder removed and had a Mediport put in my left chest because they can't find a vein when I need an IV. Recently, due to complications, I had to have the port removed, because it did not return any blood when they tried to use it. I had it flushed regularly and it flushed fine. I weighed early last year, almost 290 pounds. I am now down to 190 pounds. For the time it took for me to sit down and write this, my right thigh is numb and my foot goes from very hot to very cold. At first I thought it could be the RSDS, but the symptoms I am having is different.