What Causes Slight Syncope With Headache And Loss Of Appetite?

18 years old, 5'8, no idea of weight but overweight, feeling faint whenever I stand, or sit up. Went from freezing cold to burning up in hours. Lose of appetite. Headache, quite painful, back pain as well. All for about 48 hours, have previously had faint spells but pass quickly and only happens about once a month.