Do you have plants in there too? If so, your plants are probably using up the ammonia/nitrates. If it were me, I would probably do 20% water change every couple of days for another month, just to be safe.
Since you registered Nitrate and no Nitrites, your bacterial colony might be large enough to process the tiny amount of ammonia left over after your big water changes - in which case, your tank is "cycled" (meaning, you have a colony of Nitrosomonas and Nitrobacter present).
Try cutting your water change frequency to every 2 days (but test each day still) and see if it remains constant.