Combivit gives an instant boost but if your land doesn't give all the minerals they need you may need to give regular mineral drenches.
The whole of the UK is deficient in copper, cobalt and selenium. Some sheep are better at coping - Texels manage on very low copper, for instance, and can even get liver damage from being given too much copper.
Drenches with chelated minerals, or boluses which release slowly over time, will give a much longer-lasting effect than cheaper non-chelated drenches. You can also give licks to allow them to get extra minerals - but I'd suspect that you may need to use a chelated drench once or twice a year as well.
As others have said, if fluke has gone untreated for a period, the liver damage can be so extensive that it takes a very long time to recover, and/or never fully recovers. And the impaired liver function can make it difficult to get an effective dose into them. So going forward you will probably find it best to drench regularly for fluke whenever the beasties are active. (Most usually autumn and winter, but some enough years the conditions mean they are active in summer - and not just a wet summer, either. Keep an eye on the monthly NADIS parasite forecasts.)
Carrs Billington make up and sell fluke+mineral drenches, and worm+mineral and fluke,worm and mineral drenches, because it is so common in the north of England to need to give minerals regularly and to fluke regularly. However, the chelated drenches are a better source of minerals if it suits your system to use them. They have a good long shelf life too, and the premixed drenches are usually 6 months max.