Thanks for the query.
As all your tests showed negative results, the possibility of pregnancy
can be almost rule out.
sensation could be due to some gastrointestinal problem.
Dietary modifications like:
-Taking smaller quantity food in more frequent intervals.
-Avoiding oily, spicy food.
-Taking plenty of fruits and vegetables.
-Regular exercise etc.
You can take antacids with your doctor's advice that can help to some extent in decreasing the symptoms.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429