Taking vitamin C is good for a quick perk up, but if you are deficient in something, it can cause a chain reaction as most vits/minerals require a nother alongside it to work. So try to take iron rich foods at the same time as vitamin C to increase absorption of the iron - a glass of OJ with iron fortified cereal, or broccoli alongside meat etc, this could perk you up. Eat more oily fish too if you can as Omega 3 supports brain function and can reduce stress and anxiety.
IMO a really good multivitamin is a good insurance policy, and a good place to start. If you still feel bad after taking a good quality vitamin, perhaps you have a deficiency to be checked out..
I take Solgar multivitamins. Female Multiple when not pregnant, and currently taking the Pre-natal Nutrients for pregnant and lactating women.
I also take Higher Nature's Omega 3 Fish Oils (safe in pregnancy too as they are taken from the body, not the liver of the fish). I really notice a drop in my mood when I am not taking them, being a bit prone to anxiety and low mood as I am. They're really good.
They're expensive brands but I do feel you should pay for the best if you're going to take something, and the ingredients are high quality/purity. E.G. cheaper multivitamins use cheaper sources of ingredients, so in a standard preggie vitamin you get from Boots, you get cheaper forms of iron which can (and did!) make constipation worse, whereas the Solgar one uses a more quality one that doesn't bung you up. Or the vitamin C will be "buffered" to be more gentle on the stomach.
I also get them at discount from online chemists which helps! Sometimes just a course of a good brand like this whilst addressing your diet can be enough.
Hope you feel better soon.