Have you considered doing a Water Fast
(i.e. no food at all and just drinking water and nothing else)? When I was a student (and ate and drank a lot of junk), about 15 years ago, I suffered from gastritis and it just came naturally to me to stop eating. Actually that's how I got interested in alternative health, because I started looking for information about fasting. Ten days of Water Fasting
would really help a lot and even just four days would already make a difference.