Painful backache episodes lasting for a few weeks

[Yoddleman]

Some info first:  
    Age: 46
    Sex: female
    Height: 164cm
    Weight: 58kg
    Race: caucasian
    Duration of complaint: so far ~two weeks this time, many similar episodes in the pas
    Location: mainly trapezius muscles
    Any existing relevant medical issues (if any): started menopause
    Current medications (if any): none

Writing on behalf of my aunt - for the past two weeks, she's been suffering from back pains which seem to have the most painful spot/source of the pain on her trapezius muscles, sometimes near the cervical vertebra, other times, more towards the shoulder blade. Also, sometimes the muscles on both sides of the body are affected, sometimes just one (more frequently the left one which is the same shoulder she carries her bag on).

The pain affects the back, though never lower than the bra, and sometimes radiates to the arms though not below the elbow. Sometimes also wrist pain accompanies this.

What's interesting is that the pain always lessens substantially after night. In the morning it's hardly painful or just very mildly so, then it gets worse and gets unmistakeably painful in the evening/night hours. She describes it that in the evening, she feels like suddenly her shoulders feel heavy and then it's downhill from that, to the point of every move being painful and a slumped posture being the only way to alleviate the pain a bit when walking. Raising your arms is painful, any motion is painful. The only way for it to not be achy is to lay down flat so that your back is pressed against the bed. Aunt also describes it that it's a similar pain as if you had overstrained or sore muscles after too much activity or when you catch a flu.

Along with aunt, we became interested by this cause it's not the first time it's been happening - she had similar episodes in the past for years, usually lasting a few weeks and then going away on their own with no prior warning, just as they came. They usually happen some three or four times a year, give or take. We've tried connecting this to various activities of hers (carrying a heavy handbag, too little movement throughout the day, working on a laptop with arms unsupported) but to be honest, every time it felt like we figured it out, she would refrain from doing it for a few days to test our hypothesis out (like try not to work with her laptop on her laps but rather on a table) and it would still happen. It just seems like there's no definite trigger for the pain - the epiode just starts, lasts however long it may and disappears. We also thought about poor sleeping posture (on the back, with head twisted to the side) or poorly fitted bra (aunt said that she has marks from the bra straps virtually every day because of tight fastening) but we're not sure if this would produce such purely episodic pains instead of constant ones.

What may that be? It's not like it's hard to live with it, it's more of an inconvenience than anything but maybe you have any idea what may be causing this?

[Yoddleman]

No ideas? :(