My first attempt at iris & only flowered for two weeks.Is this normal?

Hi Snowdropfan, the answere to your query probably depends on how old/mature your iris is. If it is a young bulb then it will probably only have the energy for one flower spike this year which may well go over after a couple of weeks. As the bulb matures it will keep growing in size and energy to put up several flower spikes over a period of a few weeks giving a longer progression of flowers.
As the bulb has now finished flowering you should start to give it a weak feed of liquid tomato fertiliser every two weeks to encourage the bulb to build up energy for next year. Stop feeding and watering when the leaves die back and keep dry until September.
It would be interesting to know where you got the bulb from.