Brief Answer:
Several possibilities.

Detailed Answer:
I read your question carefully and I understand your concern.

The type of diffuse headache you describe is not that specific, meaning it can have many different causes.
One possibility is tension type headache. It is the most common type of headache affecting most people at one stage or another in their lifetime. It is a primary headache, meaning there is no identifiable cause (hence no associated danger). Often it is triggered by stress and anxiety (which could also explain the shakiness). Treatment consists in over the counter medication like Ibuprofen.

Another possibility is a passing viral infection which may commonly manifest with headache, muscle ache and weakness. Other types of infection may manifest with headache as well.
I see at some time in the past you've asked a question where you mention sinusitis. Sinus infection is a common cause of headache so especially if you have also symptoms like nasal congestion or discharge that is a possible cause.

Another cause for such headaches and shakiness could be blood pressure alterations, both high and low blood pressure could be a cause.

If you happen to be in any particularly restrictive diet that could be another possibility.

Lastly anemia, metabolic or hormonal alterations should be considered as well when no evident other origin.

So if there is no clear indication of any of the above possibilities (like sinusitis or diet) I would give it a couple more days, using Ibuprofen to alleviate it. If still persisting you should see your primary physician for a check up of blood pressure and other vital signs and some routine blood tests to check for anemia, infection, metabolic or hormonal causes (like complete blood count, glucose, liver and kidney function, electrolyte panel, thyroid function).

I remain at your disposal for other questions.

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