Here are the precautions which you can use to avoid stomach ache, pain, nausea and avoid bad health.
First, keep this thing in mind that you are not in a competition or what so ever. There is a psychological effect during the time of Sehri that impacts the individual and makes him/her think that for 12-18 hours I will not be able to eat or drink. This then creates a reaction and one starts to stuff the stomach with lots of food and water.
Please control your thoughts during the time of Sehri, otherwise if you stuff too much then believe me in exactly 1 or 2 hours you will get stomach ache / stomach pain and that my friend you don't want it trust me on this, I have been through this situation.
Second, when the time of Iftar comes near please don't imagine food and chilled water/cold drink because the reason is that if you do this, you will end up eating a lot more than usual and same reaction will start. If you don't believe this, then ask any doctor that should I eat to full in aftari ? You will get your answer.
To start take a date and take some water ( half or less glass ) then go to namaz after that when you come back start little and drink water after 2 hours of eating.
Please don't take cold drink in Iftari as it will hurt you badly because it dehydrates the body. Just go for plain simple water.
Keep the fast for Allah and you will be strong the whole day.
If you keep stuffing your stomach to full during iftari and sehri then trust me you will end up in hospital and same advice will be given to you, that control your hunger and eat light.