My Left Hand Vein Is Paining From Past 3 Days,

my left hand vein is paining from past 3 days, its starts from below the elbow and heads towards wrist and this pain is unbearable. it will be more when i am in rest position. i am just 21, and i am worried about this. last week when i consulted a doctor, he said that my blood pressures are falling down due to lack of food and water intake, he is right, i was not not taking sufficient amount of food and water from 4 months as my emotional state was too bad. but now i want to change the situation. i want my blood pressure to be normal and please tell the cure or reason for my pain in left hand vein