What u experincing is features of Hypochondriasis
... where person is preoccupied about having certain organ disease...and unable to remove this from mind inspite of no evidence supporting this and all innvestigation report coming to normal and not explained by any physical illness...type of like anxiety
There is reason to worry that it affecting ur routine...so to come out of this u need to meet psychiatrist
in person for deteailed psychiatric interview and then appropiate management will be done.
This happen due to some chemical changes in ur brain not visualised by routine imaging So pls visit to psychiatrist he will help u.