Your initial symptoms of a stomach bug and the ongoing symptoms of sinusitis, headache, sneezing, cough could all be connected with a viral gastroenteritis
followed by a chest infection
The pain in the rib is usually an inflammation of the lining surrounding the lungs, called pleura, and hence referred as pleuritis.
I hope the stomach or gastrointestinal symptoms have now cleared up and if not, you will need a stool c/s followed by a Chest X Ray to ensure there is no pneumonia; and urine c/s (if there are urinary symptoms as well).
Additional blood tests would be a complete blood count
, liver function tests, CRP.
The treatment will then depend on the results.
Typically a viral gastroenteritis does not require any therapy, but you must ensure you drink a lot of water, take rest, have some anti-emetics (anti-sickness drug) if nausea is severe.
Antihistamines such as cetirizine
will help with the sinus symptoms.
Hope that helps.