Hello,
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I can understand that you must be very concerned and upset about your chronic symptoms. Given your history, you have a condition called gastroparesis, which is the slowing of stomach motility. Gastroparesis has various causes, including obesity, diabetes, drugs, advanced age, H pylori infection of the stomach, and among a few patients as idiopathic (which means no cause could be identified after extensive workup including endoscopy).
In some patients, the gastroparesis is preceded by a viral infection of the bowel, such as acute gastroenteritis or sometimes viral infection of the throat and ear. It could also be caused by post-viral infection syndrome. This similar mechanism can cause people to develop irritable bowel syndrome, a condition with predominant pain over the lower part of the belly with diarrhea or constipation. Since you do not mention significant pain in the abdomen, I refrain from diagnosing irritable bowel syndrome.
All this information makes you understand how such things happen to the human body after only a minor viral infection.
Now, coming about management. In most cases, this will go away with time, but certain medications could help symptom control.
I recommend you to start tablet Digestine 40 mg (antacid) twice daily half an hour before meals no more than four weeks. If on day 3, you do not have an improvement in your symptoms, I suggest adding tablet Onset (Ondansetron) 8 mg thrice daily for four weeks.
Meanwhile, try to reduce the volume of your meal. Instead of three-time meals a day, take similar amount of calories six times. Try to avoid ingesting a large amount of water while having meals.
Regarding your question about the blood test. There is no confirmatory blood regular or special blood test for diagnosis. The gastroparesis diagnosis is established by gastric scintigraphy, a specialized radiology test. You will be asked to take Barium (white paste-like substance) by mouth, and they will take x-rays of your stomach for up to four hours. But given your clear cut history, I am deemed to recommend your treatment at the outset.
Since you do not lose any weight in the last few months, a gastroscopy (endoscopy of stomach) is not required at this point.
I would encourage you to meet a gastroenterologist in person to get examined physically. Augmentin (Amoxicillin and Clavulanic acid), Azithromycin, and probiotics do not seem to affect this condition. But once you are improved with your symptoms, I would recommend a safe antibiotic course for three weeks to balance the amount of abnormal gas-producing bacteria in your gut.
Please give me an update on your condition in one week.