I have put a 'tag' on this question - the tags help you to find other similar questions that have been asked in the past, like Stan's a couple of months ago:
"I am also having difficulty with maintaining weight, nausea and stomach cramps, I am 18 months post op".
So I think it would be worth seeing some of the suggestions, like Larry's, that were made in response to Stan's question.
There is medication called domperidone that helps with wind and getting the food to pass through the system at the right speed (some people think this is a fantasy for them nowadays, but the medical term is motility!). It has to be prescribed, and I think that you would be wise to check with your specialist nurse, or even better a specialist dietician.
Low glycemic index foods may also help.
Keeping a food diary is a chore, but not as bad as having to put up with stomach cramps.
If you are in doubt about grapes, stop eating them for a while and see what happens.
There is some useful information in the OPA booklet 'Life After Surgery' that you can download opa.org.uk/ and if you ring the helpline 0121 704 9860 they will send you a recipe book.
The CORE factsheet on dumping syndrome is also useful. corecharity.org.uk/Informat...
And some more information at sosg.info/diet.aspx
You probably have enough information to run with for the moment, but please come back and let us know how you are getting on with the problem.
Good luck with it!