What Causes Persistent Nausea, Fatigue And Headache?

Hi, I'm a 15 year old girl. I'm about 5'4 and 115 pounds. I have had no medical problems in the past. Recently I've been starting to feel really weak. It takes a lot of energy to just stand up. I have constant headaches and my eyes always feel strained. I feel queasy and nauseas and have random moments where I sweat profusely. I'm a vegetarian, in case that might have anything to do with it. I have no idea what's wrong, so I hope you can help me. Thanks!