Brief Answer:
Try antacid, activated charcoal and liquid diet with probiotics.

Detailed Answer:
Hi.
Thanks for your query.
Noted the history and understood your concerns.
The commonest causes of pain which feels like tightening or being full without eating are:
Gaseous distension of the intestines.
Sub-clinical intestinal infection.
Stomach flu.
I would advise you the following in such a situation:
Try Antacid when on empty stomach, activated charcoal, soft bland diet or liquid diet and probiotics and see the results.
If there is no relief, it is better to get a clinical evaluation by a Doctor and few investigations of blood, stool; X-ray of abdomen and ultrasonography to get an appropriate diagnosis and have proper management to get a relief.
If a specific cause is found, it will be treated by your Doctor to give you a cure.

I hope this answer helps you.
Please feel free to ask for further relevant queries and give feedback about:
Any other symptoms like nausea, vomiting, loose or hard stools?
Any acidity related problems?
Stress or anxiety?
Any outside food or beverages that you had before starting the problems?

Awaiting for your feedback.

---