Brief Answer:
an impending infection in the body.

Detailed Answer:
Hi,
Thanks for choosing 'Ask a Doctor' service for your query.

Chills usually occur at the start of an infection. They are most often associated with fever and nausea. Chills are a natural mechanism of the body by which it raises its temperature to remove bacteria's as bacteria could not survive in high temperature. Chills often predict the coming of a fever or an increase in the body's core temperature.

Feeling week and nauseous is suggestive of ongoing infection in the body.
Very likely it's a bacterial infection.

Suggestion-

Take a broad spectrum antibiotic like Ciprofloxacin in dose prescribed by your doctor. This would kill the bacteria.
To control nausea, you may take Ondansetron (eg. Zofran) 4mg three times a day it's over the counter.
Tab ACETAMINOPHEN (Tylenol) should be taken in doses of 500 mg thrice daily.
Drink plenty of water and electrolyte-rich drink.
Take a soft diet.

Investigations suggested are complete blood count, ESR and CRP to rule out infection.

Hope you would be relieved soon.
Follow-ups are most welcome.
Regards

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