I have a problem if I eat too much. (I know what your saying......don't eat too much), but I only have small/medium sized meals, meat and two veg, nothing too fancy. My problem is that should I take in a bit too much my stomach really hurts. Goes hard, painful to touch and aches really, reallybad. To the point on taking a strong painkiller. The pain also radiates round my side and back. Could this be IBS symptoms
It could be ibs. Maybe try changing what you are eating for a while. Some meats, fish and chicken etc are more easy to digest than red meat and some veg is very hard to digest. In fact when I have a flare up i have to avoid fruit and veg completely because they make it worse. try going for a week with just bland food, white meats, eggs (not fried), white rice, cooked oats, soups/broths (no creamy soups) and toast/crackers (if you're ok with bread and natural/bio yogurts and some people find mash potato and good one. Start with small amounts like you are used to and try to gradually build it to what you would consider a 'normal' portion size for yourself. If you find yourself wanting fruit and veg try cooked apples, (can even make a crumble type mixture from porridge oats, with cinnamon etc), soft well cooked carrotts, bananas, some people are ok with berries. And i would suggest avoid salad as this can bloat people but Its really trial and error when you start putting foods back into your diet. Take it slow and dont be too alarm or disapointed if you back track a bit and need to eat bland again for a while. I know its boring but getting yourself back onto food again is the most important thing. While these foods are predominantly my diet I can now add, fruits and veg in and have the occasional piece of non fatty red meat should i feel well enough.
The most benefitical thing ive found is to find the one food you can snack on when youre feeling iffy. Mine is wheat free ginger biscuits. Im not amazing with wheat and ginger is good for digestion. Similarly, things like herbal teas (research a good one for your symptoms, some say peppermint works well but it really doesnt for me.. again trial and error) And sometimes i find a small amount of yogurt before a meal helps coat the stomach and i find it easier to eat (although this may just be in my head :p)
Ive been going through this now for 5 year), I've read everything and tried to do everything. It is just really trial and error. 
Good luck. i hope something here was helpful 
Look up FODMAPS diet in the internet I am on it since last May and it has made a huge difference to me far less pain, bloating etc. In April/May I was in agony after some meals. I am not there yet but I am encouraged by improvement. Good luck.
Thank you both for taking the time to reply. I guess my diet needs to be changed and may be beneficial in eating little and often, rather than one large meal. I have tried the peppermint capsules, but they made me feel very nauseous.
Im going to look up Fodmaps on the Internet, hopefully this will be able to reduce my sysymptoms.
wishing you both well