The symptoms you describe could be so many things. But since it has gone on for so long and you say it has affected your quality of life, you really need to go see a Gastro Doc. or Doc of Int. Med.
We could guess hundreds of things, and suggest numerous things for you to try, but never get it right. Why prolong your suffering and potentially incur irreparable physical damage that way.
I don't wish to sound overly melodramatic, or scare you with the following. Your post hits very close to home with me, please indulge me and my soapbox, if you will.
My sister had 'stomach' problems for a few years during secondary school, college, and university. Her symptoms were vague and not always exactly the same; bloating, discomfort, occasional 'stomach virus', and sometimes stress seemed to make it worse. However, she didn't wish to take time away from her studies and work for a doctors visit. (In reality she was avoiding/fearing hearing bad news.)
She FINALLY went to the Doc after finishing her Ph.D., only to discover she has Crohn's disease. BECAUSE OF HER DELAY, her small intestine is riddled with scar tissue. She has numerous fistulas, and has permanently lost use of a third of her intestine.
Now, some of that damage would have occurred naturally due to the disease. But, her delay in getting control of the problem allowed it to progress far more rapidly than necessary.
Do yourself a favour and get checked out by good doc, or better yet a good G.I. doc.