I have a burning sensation that comes and goes at the back left hand side of my head and a little down the back of my neck. it feels almost like acid. it is not painful but rather disconcerting. ?

Burning : A burning sensation like acid flavor support gastritis, and I recommend taking tums (calcium carbonate) over the counter and see if this helps. Try to avoid chocolate, acidic foods, tomatoes, lemons as these can worsen gastritis or GERD

Pinched nerve?: Hi, perhaps a pinching, or irritation of the C2 / C3 nerves that supply that area? Take some time, notice if there is pattern to this, worse with certain activity / posture? Eased by Ibuprofen? Does it come more often in periods when you are under a degree of physical / mental stress? If it persists, becomes severe, or you get similar symptoms in other parts of your body then do see your GP