FTM need advice.

What are your experiences with milk AND soy intolerant/allergies? We switched from Similac Advance to Similac Soy Isomil at about 2weeks....now week 3 and tho the gas isn't as bad, it's still there. It still sometimes looks like she's struggling during feedings and doesn't puke but is a very "messy eater" always wiping her face off throughout a bottle...now she's got red rashy dots on her bottom around her anus. I'm irritated because AGAIN I just bought two containers of formula and now thinking we may have to switch again. But to what? Is this rash food intolerant related? Am I going to be stuck buying some crazy expensive formula?

Also have finished the Huggies we got from shower and started using the Luvs this past week, didn't like them so tried the pack of parents choice...I still prefer the Huggies so I'm not longer going to use the other brands and bought her more Huggies. Don't know if this could be diaper related so thought I'd throw that in. We use rash cream every. Change as well so that's not helped it.