What Is The Treatment For Severe Leg Pain?

I have been having leg pains for the past 3 days in my right leg. The pain begins at my hip and goes down to the heel of my foot. It hurts continously wether i'm sitting, standing or laying down. I have not had any recent injuries but I have had the birth control Implanon insterted about 3 weeks ago and I'm not sure if this can be a cause. I also have a noticable vain on the side of my knee...I was told this could be the result of a bloot clot and I need to know if it needs immediate attention.