This plant needs slightly acid peaty soil. It maybe with the unprecedented wet weather the ground may be waterlogged and any goodness leached out of the soil. I assume it is not large and could be transplanted to a large container with fresh compost and good crock drainage. This could be kept outside if there's not a severe frost and when the plant has 'perked up' can be replanted in more fresh slightly acidic compost in the position of your choice. .