What Causes Frequent Headaches,dizziness And Itching All Over The Body?

Hi my name is brenda im 18 years old and i resently had a baby 5 months ago but i have two kids my question ever since my daughter was born ive been having diffrent symotoms witch worry me i get freaquent headaces almost like a migrane and if i sit for at least five mintues and stand up i get very dizzy almost to the point where im going to faint,i also expirience itching all over my body almost like an allergic reaction but ive never been allergic to something what could i have?