Agressive Bees

In my fourth year of bee keeping and have never had bees this agressive. I did a split on a hive that had a heavy bee population with plenty of room but seemed to be likely to swarm. In my experience if the two deeps are packed with bees, it doesn't matter if you have one or two medium supers on, the hive will still swarm. However, this year after doing the split, shortly thereafter, one would hear a bee (sounds like a drone) and it would lock onto you and it would either sting you or you would have to kill it. I would be no where near the hives at this time. Shortly after this bee was taken care of either by being killed or stinging me, you would hear the buzz of another bee and it would react the same way. They would follow you where ever you went with one of the two results. Then you could be outside for 4-5 days without incident and then the same process would repeat itself. I have read and heard that requeening is often needed to solve the problem of aggressive bees; also heard that if a hive is queenless (even if a queen cell is present??) they may become more aggressive. Any thoughts or similiar experiences??? Thanks.