I have been getting headaches, stomach aches and dizzy spells. And I am very moody. Why?

Needs Evaluation. You need more evaluation. You may be just having a viral illness or you could have some problem in your head such as a tumor. Don't waste time researching on the web. Start with a primary care doctor. They may send you for additional studies or get a neurology consultation.
Exercise. It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor and discuss if you may be depressed. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated.