Winnie, if you look through the peer reviewed, medical/nutritional journals you'll find lots of conflicting information about this. IOW for some people the nightshade family causes problems but for others, like myself, they can eat them without any problems. I eat plenty of nightshade veggies including potatoes, tomatoes (tons of those daily, love them), eggplant, peppers etc. I know that Dr. John McDougall, as part of his elimination diet also suggests citrus fruit and gluten (wheat etc.) as potential problem foods to test.
The way to really know if it affects you personally is to do an elimination diet where you eat a very limited amount of foods least likely to cause problems and keep a diary. You add a new food only every couple of days, watching to see if you have a reaction before adding something new again. It's commonly suggested by pediatricians when young children have problems. It can clearly pinpoint those foods that truly cause problems as you eliminate any possible confusion that can occur when eating lots of different foods.
Or you can avoid all of them and see if that makes a difference - you won't know until you try and it certainly is worth trying to see if it helps.