Brief Answer:
As detailed below.

Detailed Answer:
Hi.
Thanks for your query.
To recapitulate: Female/19 - intense pain by her ribs on left side - one bout of brown vomit - light fever - not feeling well - pain pill helped a little..
The commonest cause as per the history you have provided about your daughter are:
Viral infection causing costochondritis.
can be beginning of gastroenteritis hence causing the vomiting and pain on left with fever

I would advise her the following:
- First of all, to check for the contents of vomit as it was brown- was it something she ate/drank or due to presence of altered blood .
- Secondly, watch for loose stool and black color of stool- if so send the sample for tests including that for occult blood.
- Get her started on a PPI like Omeprazole.
- Give her antacid and may need medicines like Domperidone if the nausea/vomiting persists.
- Give her Tylenol, avoid Ibuprofen like medicines as it can cause/increase acidity/gastritis
- Get the blood, stool tested and ultrasonography of the abdomen and X-ray of the chest as the pain is on the ribs and can be due to inflammation of the lower pleura and/or lung on left side.
- Further treatment as per the clinical evaluation by a Doctor, clinical findings, reports of the investigations, further investigations and treatment as needed.

I hope this answer helps you both, please feel free to give feedback and ask for further relevant queries if you feel that there is a gap of communication.

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