Fruit dropping from lime tree

Hello everyone, me again.  Does anyone know if there's a reason why my little lime tree would be dropping all of the developing fruits?  They get to about a centimetre long and then fall off.  When I bought it last year it had about 10 fully developed fruits which I used.  This year it's put on about 6inches of growth and lots of lovely flowers but the little fruits just keep dropping off.  Any ideas?  Many thanks.