Hi welcome to Health care magic forum. most probably your problem may be some fold of the ureter, or mesentric herniation into the posterior abdominal wall. the drugs you are using will controle the pain but wont cure it. Of course they wont have any side effects in future. the side effects of the drugs are not applicable to you as they would have shown by this time.
I advise you to consult a general surgeon , he canhave overal idea and may find the problem.
Besides i advise you some non medical procedures for relief as divertion procedures as yoga, meditation, reading books, hearing music, and if interested gardening.
Diet recomendations as see that you pass stools daily by taking green leafy vegetables, pulses, sprouts. avoid taking spices, chillies, junk foods, and oily foods. Wishing for a quick recovery and thanks for calling.

Hi friend,
I can understand the pain that after having all the investigations and consultation regarding the stomach pain, it is still there and the stress associated with it. Some times it happens that some type of pain is functional in nature and you will not find any physiological or pathological explanation for that problem. These types of problems further deteriorate because of stress associated with it. So one important suggestion for you is that try to make yourself stress free because of that.
Another important thing I would like to suggest you to consult some gastroenterologist regarding this problem and ask him to look for Irritable Bowel Syndrome (IBS). IBS can present in very vague form and this can be the problem with you.
Most of the medication right now you are using is for the symptomatic improvement of your condition. Colospa Retard and drotin ds are mainly decreasing the motility of your gut and help in relieving the pain associated with abnormal gut motility. Normaxin has combination of drugs which helps to reduce your stress level and have some anti ulcer effect. Mebex has mebendazole which is drug to treat worm infestation. So all these drugs are mainly help you in relieving the symptoms you are having and of course there are various side effects associated with these drugs.
Thanks and hope this will help you.