Problems with atrial fibrillation

Hi im a 37 male i have sinus tachy and take 100 mg of atenenol per day to control it. last oct 2012 i went into afib and was converted back with iv meds, with in 36 hours of the onset, there was a battery of tests echo, stress test, ekgs and coritid tests and everything was normal . No known cause therefore no additional treatment was given, im still not on a blood thinner i just take asprin before bed. Now fast forward to oct 11 2013 its 9 pm im laying in bed and my heart goes into afib again, i go to the heart hospital we have on long island and i get meds via iv and am given a pill call rhythymol i was given 450 mg of this and my heart converted about 5 hours after taking the pills. still no cause for the afib , Know both times i had a headache and was dizzy the week before the episodes occured, so i think i had an infection prior to the onset + at the hospital the cbc blood they did showed high wbc but no one said anything to me . if in fact i do have an infection can this cause afib and why can no one find the infection ? im going to follow up with my cardiologist. what tests should i ask for to get to the bottom of this? Thanks

1. Reset the rhythm or control the heart rate
2. Prevent blood clots

Treatment includes the use of Beta blocker medication and correct low Potassium and Calcium blood levels.If persistent for more than a few days, a blood thinner may become necessary to protect against the risk of thrombus (clot) formation, that can cause a stroke.

Generally, all new onset AF should be managed with a blood thinner such as Warfarin (Coumadin) to protect against blood clots that may cause a stroke, Pulmonary embolus (PE), or a clot to other parts of your body. Atrial fibrillation, especially if not controlled, may also cause heart failure. 

Because the use of blood thinners may cause bleeding in other parts of your body, its use should be considered carefully. Likewise, new medications may also carry specific risks.