Often, the cause of pericarditis cannot be determined, in which case it is referred to as idiopathic pericarditis.
However, it is often a complication of a viral infection.
There are some lab tests that can be done which may help point to the cause:
*A complete blood count may show an eleveated white blood cell count, which is a marker for infection
*Blood culture
*ESR
*CRP
*Pericardiocentesis, with chemical analysis and pericardial fluid culture
If you do get any of these lab tests, be sure to tell your doctor and/or the lab staff that you take indomethacin.
To answer your question about indomethacin, you should drink alcohol only in moderation with this medication (ideally you should not drink at all). Drinking more than 3 alcoholic drinks a day may increase your risk for stomach bleeding.
In terms of aspirin, it can interact with your indomethacin, so I would not reccomend taking the two together without talking to your doctor first.