If you can collect a sample from your breeding sheep and a sample from the lambs, that will be helpful.
We don't routinely worm our breeding stock except at lambing time now.
Don't forget about fluke too. A FEC won't show if you have fluke or not, and given your location, you will almost certainly have it on your land. We fluke breeding stock routinely about now, at scanning in January and at lambing.
Remember to tell your vet when the lambs are going off - some wormers and flukicides have long with drawal periods. Triclabendazole, probably the most widely used flukicide is about eight weeks, I think.