At the very least you should be taking vitamin D. There is a lot of research that suggests we don’t get enough through sunlight especially in winter. Why don’t you go to somewhere like Planet Organic or Wholefoods and talk to one of their advisers about what in particular you’re trying to improve. B12 and iron might also be necessary if you don’t eat much meat.
If you have specific symptoms you should go to your GP for a blood test. Long term conditions such as Vit D deficiency or Pernicious Anaemia need prompt treatment. But agree with previous poster that multivits bit of a racket. Your body can’t store many of them so ‘superdoses’ may do more harm than good.