Brief Answer:
Urgent clinical examination by a Doctor and investigations

Detailed Answer:
Hi XXXXXXX

Thanks for your query, albeit small.

To recapitulate:: 39 years male is having migraine since Sunday and taking Dolo-650 - severe pain on under the 'right rib-cage bottom' - wants to know the cause and to know whether this is appendicitis - wants to whether to undergo some tests...

I would like to know a few details for me o answer you more appropriately:
-Since when have you got this pain?
-Any associated fever, nausea, vomiting, bloating or fullness of abdomen ?
-Any referred pain to other sites of chest, shoulder or lower abdomen?

The commonest causes of pain under the RIGHT RIB-CAGE BOTTOM are :
Cholecystitis- gall bladder problems
Liver problems
Duodenal / Gastric ulcers
Gallstones on gal;l bladder or the bile ducts
Rarely pancreatitis , colitis and so on.

I would advise you the following :
Give the complete history to me and the attending Doctor, who is going to examine you.
Go to the nearest hospital / Emergency room (ER).
Get a clinical / physical examination by a Doctor, preferably a General Surgeon.
Urgent ECG - this is important to rule out cardiac problem
X-ray chest
Ultrasonography- helps in diagnosis of gall bladder, live, pancreas and all other organs including appendicitis.
Blood investigations : CBC, liver functions, urea , creatinine, Lipase & Amylase, CPK
Urine tests.

An examination by a Surgeon and all the reports together can decide the diagnosis and plan for a further treatment.

Appendicitis : the pain starts in the upper abdomen and may shift to the right lower abdomen along with other symptoms. This is is usually not seen under the rib-cage bottom if this is what you mean by- the upper abdomen. Ultrasonograhy and CT scan can confirm.

I hope this answer helps you to get a proper diagnosis , come out of the emergency and get a proper further treatment. Please feel free to ask for more or if you need further clarifications if you feel there is a gap of communication.

---