Not eating can reuslt in a n ulcer and if you have one, it will only make it worse. I wonder why you dont want to go to a Dr. Simple medication can get rid of your ulcer and you will feel a whole lot better.
Also stress can irritate an ulcer as well. A Dr. Can give you meds for the ulcer and help you eat healthier and manage stress in your life to keep the ulcer from coming back.
On the other hand, is there a reason why you have not been eating well? Have you been sick with something else? Effort to lose weight maybe? Like I said, this may also cause an ulcer.
Please see a dr, or at least write back on why you dont want to see a Dr. And someone can give you other suggestions maybe. Right now probably everyone will tell you to get Dr. Help.
Take care and hope you feel better.