Hi. Thanks for your query. Noted the history of a 16 year old male, weird sensation in the lower abdomen on left side on waking up in the morning, like something is moving inside, have normal diet for age, do sports regularly and pretty fit; wants to know what is this.... The most probable cause of such a weird feeling is sort of colitis, irritation of the colon in the morning as it happened in the morning after getting up. Although you have not mentioned anything about the bowel movements, I would advise you the following: Watch for the bowel movement, the color, odor, consistency, blood, black color and so on and in fact it would be better to send the sample of stool for tests. If the symptoms persist or increase with additional symptoms, get a clinical evaluation done by your Doctor. Earlier the better, why wait for more problems? Then get X-ray and ultrasonography of the abdomen and take the medicines as may be dictated by the symptoms, signs and investigations reports to get well soon.