If heart has been ruled out what else could cause lightheadedness, breathlessness, bad breath, excessive sweating, night sweats, chest discomfort behind breast bone, neck pain and upper throat pain under chin? what should i ask to have checked next?

Your PCP?: If you have a PCP, he/she should be able to help you in managing almost all your symptoms, which are difficult to attribute to any one disease. So let's handle them one at a time. This requires you to make a list by order of magnitude or severity to your mind. Some of the symptoms suggest an element of stress either in your home or work life. For this I would suggest that you exercise(walk) daily