I'm 13 and have been experiencing the same thing . They do so many test and still can't figure out what is wrong with me. I feel like sometimes i'm making it up but then I notice it just honestly hurts really bad. What is helpful is to make a stomach outline or diary and explain if the feeling is worse at what time of day or when you do or eat something. I believe it could be Irritable bowel sydrome but I have no idea. Good Luck
I would suggest you switch from pepto bismol to alka seltzer, it will release the gas in your tummy that is causing the bloating. The pepto can make constipation worse. Constipation is hard on a person, altho I think gas is probably causing your sensation of chest pain. To quickly end the constipation you can try a couple things. At the drugstore you can get pre-prepared plastic enemas and also Baby Lax, the lax comes in a real small box. You can try the enemas a few times one day and see if anything comes out. If that doesn't work, the next day take two ointment tubes out of the lax box, squirt them in and waste will come out in minutes. You can repeat as needed.
To get your digestion back in order, I think you should skip places like MacDonald's and eat at Subway instead, get the wheat kind of bread, with lettuce and tomato. Eat more fiber daily, stuff like Cheerios with Acidophilus milk on it, 100 percent whole wheat bread, eat fresh fruit like blueberries for a snack, and the bran you're eating - cut the amount in half. The acidophilus milk helps break down waste. Also, every day for a while, drink several extra glasses of water, and do some form of exercise, even if it's just simple stretching, although long walks are best.
I hope this helps you. It's okay, lots of people get constipated throughout their lives, it is most annoying, but if you can get the waste moving by doing some of the things I've suggested, you should be good to go.