Is there a way at home without ever going to the doctors, to find out if i have an abnormal heart rhythm? especially few seconds after exercise?

Yes: Simply feeling your pulse, counting the number of beats in a minute and determining if there is any irregularity of the rhythm can reveal abnormalities. Your heart rate should be between 55 and 90(varies among normal people and I don't know what's normal for you) and the rhythm should be quite regular. See your MD if your rate and/or rhythm is abnormal.