Hello,
Dark circles under the eyes are temporary and caused due to insomnia,smoking, a family history of dark circles,deficiency of vit K in diet,allergies like sinusitis and eczema,pregnancy and menstruation,increasing age, medication that dilate the blood vessels and adrenal gland disorders.
Take rest adequatey and eat healthy nutritious food containing lots of green vegetables. Try to avoid caffeine, because it promotes water retention and leads to the dryness of the eye.Apply almond oil or skin creams containing vit C or K,alpha hydroxyl acids and kinetin.Also take multivitamins and iron supplements for some days and see if the symptoms improve.
Hope it helps.Take care and pls do keep me posted if you have any additional queries.
I am also a Vegan, and I have started to get dark circles under my eyes as well. I am not sure what causes it, But I would also like to know why?