Hi Emse.
What race of bee was the original queen in your 5 frame nuc?
Temperament quite often goes downhill somewhere down the line if you cross one strain of bee with another.
AMM crossed with Carnica has a particularly bad reputation.
If your colony has developed bad temper associated with a change of queen I would wait until next spring and then requeen with a queen from a local beekeeper who keeps the type of bee prevalent in your area.
If you get a bad tempered colony - and everyone does from time to time - you have to bite the bullet at some point and requeen it.