Need more information really, such as where you are, what variety of plum, but generally, because plums flower early, often the flowers get caught by late frost and don't survive long enough to be pollinated and for fruit initiation to occur, particularly in colder, northerly gardens. This year has been particularly cool, so that might explain the problem of lack of fruit, but, as I say, without more info, hard to be definite.

As for curling leaves, likely its Plum Aphid, probably the leaf curling variety - paste the link below into your browser and read the info contained there

https://www.rhs.org.uk/advice/profile?PID=681