Hurting when I eat...

For the past 3 weeks.. My I've been feeling aweful first it started out my stomach felt like there was a pit in it and just hurt and I'd have really bad head achs,and I'd have to eat every 4 hours other wise I'll get light headed and shaky and now for the past week nothing sounds good to eat and when I do eat it hurts all the way down from the time I swallow until it reaches my stomach and afterwards I'll throw it up and I've been really tired no matter how much sleep I get.