What Causes Burning Sensation From Knees Down To The Shins?

at the begining over the year i hurt my back as it turns out after having an MRI i have a bulging disc in the l5/s1 which is touching the siactic nevre which is why i have pain down my leg, but 6 weeks after the injury a started getting a tingling sensation in my face which now is a numb burning sensation around my mouth/lips chin and the tip of the tongue, it is with me 24/7 most of the time it feels like im breathing hot air and i get chests pains occasionally, 4 weeks ago from my knees down my shins to the top of my feet have started this tingling numb almost burning sensation, my gp doesnt know what it is. i have hypothyriodism but blood test came back normal have had a full blood count done and that is normal, had blood test to check autoimmune things and they come back in the normal range. i am on ampitripline but the only thing that gives me relief is a xanax and i only got those because to begin with we throught it was stress/anxiety and i was having panic attacks, i dont have panic attacks as such but this sensation is with me all the time and having a 0.5mg of xanax at night helps relieve the sypmtoms to the point that i can deal with them and get some sleep, with out the xanax i toss and turn with the discomfort of these sensations. does any one have an opinion of what could be wrong with me. i am at my wits end with this,