Hi :) I was losing weight REALLY fast when I first went on the diet. I am considered underweight too, so I didn't want to lose the weight.
I don't think that you should be eating whole wheat breads. Often times, these breads are filled with high fructose corn syrup and sugar. Even some of the brands you trust, like Sara Lee, are really made from awful ingredients. Don't let whole grain bread fool you! They only have to be made with 51% whole grain flour to be called whole grain. That means 49% of the bread is made with the white processed flour. Some of them use dehydrated cane juice or agave nectar. If you MUST eat bread, Ezekiel bread is probably the best. It tastes like cardboard, but it will be the best option for you.
Anyway, to keep weight on, I add a lot of olive oil, sesame (not toasted) and coconut oil to my food. I also eat a little bit of brown rice, hummus, quinoa, and sometimes red beans. That seems to work for me. I don't eat meat, but I eat eggs. The first week on this diet was AWFUL! I lost a ton of weight, I fainted, I threw up... but I seem to be adjusting better. I stopped losing weight and I feel amazing.
I also think that you should try to do a parasite cleanse too. I have been reading so much on here, and I am trying to get rid of parasites while doing the candida diet. I just received humaworm in the mail and I am on my 3rd day. I think that there are other parasite cleanse programs that you can look into, but I liked this one the best.