No one has figured this out in 20 years of my life

Hi I am a 36/m and since about age 16 about 1 or 2 times a month I get a severe headache only on the left side of my head. The pain is migraine level and totally takes me out of doing anything, all I can do is lay in pain. It always starts with my left shoulder-blade getting tight, it gets tighter and tighter throughout the day and eventually moves to the left side of my neck. My left should seems to rise up towards my ear to where if I am standing looking at you and my arms are hanging at my side my left hand will hang 3 inches higher than my right. My throat gets tight, I get a runny nose and the need to urinate frequently most times. My head begins to throb and severe pain behind my left eye. For years absolutely nothing works to get rid of it except a hot shower to dull the pain, but as soon as I get out it tightens up and begins again. I have been told perhaps a blood vessel on my left side was getting cut off during this shoulder muscle spasm? For now I am being treated by using a muscle relaxer called cyclobenzapine which seems to really just knock me out and allows me to sleep. When i wake up the severe pain in my head is usually gone and I have what I call a headache hangover. My head is dull, I feel out of it and my shoulder is still sore but not as tight. Has anyone else or does anyone know of this....is this just a muscle thing that messes with my brain when it flares up?