Logan had issues with dog food too. He had very loose stools, mud pie like (gross I know). I tried him on multiple brands of kibble over the span of 3 months or so and they all had the same result. I know now that it takes several months for the "side effects" of kibble to completely clear their system, but at the time I wasn't aware of that. Instead of continuing to try kibble after kibble I ended up switching him over to a raw diet and he's made a complete turn around. That's something that you can consider if you feel comfortable with it.
If you want to stick with kibble you should know that both Iams and Eukanuba aren't great quality dog foods. You may want to do some research on higher quality foods, preferably grain free. It may take some time to find one that agrees with him, but it sounds like he may be dealing with an upset tummy. Does he vomit at all?
Mandy, loving mom to...