Bulking with severe ibs

I have been weight training for years however in the last year i have been diagnosed with IBS which has stopped me from eating half as much as I used to. I have lost a considerable amount of muscle and weight and i was wondering if anyone has any bulking tips for someone with IBS. I cant eat gluten or dairy, and I have found even vegan protein powder messes up my stomach! I used to eat around 3000-4000 calories a day whereas now i barely even eat 2000 a day. If anyone has any bulking tips for a similar situation it would be greatly appreciated. Thanks