I treat mine 3 times over winter, pre tupping in october (treating for early immature fluke), end of January (treating for immature fluke) and and then again just before the girls get turned out end of March after lambing (treating for adult fluke).
There are different fluke treatments to cover the different stage of fluke throughout their life cycle. I use a triclabendazole based flukicide for the first 2 treatments such as Tribex (cost about £45 for 2.2 litres and works out about 30-40p each per dose) and for the final one I use an wormer that covers adult fluke such as Rycoben.
It'd be worth speaking to your vet to see whether you're in an area at risk of fluke and if they could just supply you with 4 doses each time rather than buying a bottle. We've never had a liver problem but for 30p each I'd rather be safe than sorry as we've had a lot of rain this year and they're in a field near water / ponds. The NADIS and SCOPS website provide some good info !
Hope this helps !! Still learning ourselves
