AF is not acutely dangerous but you do want to maintain the aspirin per the doctors instruction to reduce the risk of a
stroke for now and ask the doctor about switching to anti-coagulation meds. Because yours is paroxysmal AF, it is hard to correlate it to anything else including strep. For some people, there are triggers such as caffeine, alcohol, hormonal changes, etc ... Also, endurance training could trigger remodeling of heart muscles and some will develop AF from excessive training.