Wish you a very happy KC b'day, May lord Sri Krsna & Smt. Radha Rani blessed you always. We pray to supreme personality of godhead (Krsna) that this is your last birth in this material world & you never take birth again in this material world.
Concentration will come on its own...don't force anything on yourself. Love for Krishna is enough...sing songs for him and be happy...don't get entangled in complexities. Do not worry about concentration...give it time to develop.