It is difficult to tell from your description what you might be having. Sensation could be as result of a floating mass which could be as a result of an ovarian cyst
( very large one). Also it could just be your nerves playing tricks on you ( abnormal nerve stimulation) and could be nothing to worry about.
An intrabdominal mass of unknown origin could be responsible (maybe uterine fibroids).
My suggestion is get an abdominal scan done and get doctor to examine it closely.
Hope this helps