Answer:

It is tougher to make gains in muscle mass when you've got the conditions you've got.

For eating, you should focus on getting plenty of protein from sources you can tolerate well. Also, get as many of your calories from natural sources of food (no processed foods). Eat smaller, frequent meals so that your system doesn't get bogged down with digesting.

As far as training goes, that is a bit tougher. I would recommend my variation of density training that I call Time/Volume Training, which you could also use to great effect. It manipulates rest periods while keeping reps to 3 reps per set.