What Causes Dizzy Spells Along With Light Headedness While On Birth Control Pills?

Hi I am on the pill ( birth control) for mood swings. I got told I might have a little bleeding once in awhile but I have had my period for at least a week in half I have at leat 12 pounds and today I keep having dizzy spells and feel light headed a lot. Do I need to see a doctor. I have been told that if u have severe symtoms you should she a doctor because of blood clots and other bad things