I don't know about the MG being a factor or not.
But maybe someone can check to see if a trigger point is part of the problem?
If they just feel & push around in the areas shown on the chart below , it may help figure out if it is a strain or something else.

This chart in the link is for a therapy tool that is sold, but the info chart is really helpful too.
A friends thumb or a tennis ball or such against the wall, or on the floor works just as well.
http://www.pressurepointer.com/pain_reference_chart.htm
http://www.pressurepointer.com/Rhomb...ger_points.htm