I do not know about your bloating but it is a problem with you, not grapes. There could be a lot of stuff that is dried and hardened that needs to absorb a lot of water so it can be passed. The book, The Grape Cure, costs about $5. Here is a link to find out more about the book, The Grape Cure.
Also if you eat a lot of it on an empty stomach, do you feel a stomach cleansing action going on? I and others I know feel this. It feels like a detergent action on the stomach. I think it has to do with it being a unique sub-acid fruit. Also for 500 years in Europe they have had grape cure centers.
But now we do know that the fruit of the red grapes and grape juice contains resveratrol. Of course people think that a resveratrol supplement is as good as eating grapes. I feel that one orange is healthier for you than a whole bottle of vitamin C. This is the thing (resveratrol) that they say makes red wine so good that you should give it to your little kids so that you and them can have brain cells killed and livers destroyed.