Kudos to you for trying to keep things safe and natural. It can be difficult sometimes, but worth it. I hate to say it, but DON'T TRUST 7th GENERATION DIAPERS TO BE WHAT THEY SOUND LIKE THEY ARE! I love and use most 7th Generation products, and while I can't say whether or not the diapers actively caused your son's rash, I can tell you that they are just like any other disposable diaper you get at Kmart or the Grocery Store etc, and I can tell you that during the times that we used them, my daughter did get rashes. While white, many other diapers including Huggies don't use chlorine for the bleaching process either, yet that is one of 7th Generation's big ad claims about their product. Additionally, while their other cleaning products etc. are biodegradable, their diapers and wipes are not. They are exactly the same as all the other diapers in your regular store. They are made from the same materials and are just as bad in the landfill. The main difference is that they COST MORE than the diapers and wipes they pretend to be so different from. Aside from reading and checking out and using the products myself a few times, I have gone head to head with 7th Generation representatives at the Green Festivals, and they admit that this is all true of their diapers, but say "We can only try to fix one thing at a time." or "We plan to address that in the future." but they never do and they won't until enough people call them on it! I've been complaining at them for 5 years now! (Sorry for the rant, but disposable diapers are a "hot button" with me, and it irritates me that 7th Generation is so misleading about this product.) :) Anyway, some companies to check into if you really want an alternative diaper are 1.) Nature Boy and Girl if you can find any. At the start, the company underestimated their demand, weren't able to fill it, and had to close. But there have been rumors here and there that it will be restarted. Nature Boy and Girl diapers were terrific. My daughter never got rashes, they had no bleach or gel in them and they were made from Bio-film and absorbent wood-pulp fiber so they were 100% compostable (if only urine) and 100% biodegradable. 2.) G-diapers were great! (www.gdiapers.com or Elephant Pharm. Don't know if Whole Foods still has them. They went full on for 7th Generation to be their "keystone" despite the fact that some of their employees know the problem with them too.) G-diapers come in cute colors. They are comprised out of a totally washable, cotton outer diaper with washable snap-in nylon liners. You keep the diapers and liners and buy absorbent inserts that are totally natural, 100% flushable, compostable and biodegradable. We loved them. Initially a small investment to get the diapers and liners, but by the time you've purchased several packs of inserts you are saving money. 3.) Tushies are unbleached and use the absorbent wood-pulp for the filling. The outer shell is like any other diaper and not biodegradable, but they are a "lesser-evil" compared to some of the rest.
As for the rash, I'd have a doctor double check it if it's really persistent. Baby powders with talc aren't great, and can cause irritation for some kids. On the flip side, the natural cornstarch based powder can help harbor bacteria against his skin if his diaper is moist, thus causing a bacterial rash, or he could have a sensitivity to a plant extract in the product although that would be a less common problem. Many natural remedies can work, but it's important to be sure of what you are treating. I can't recall if I've read a label for Earth's Best, but I've generally been happy with their products. Burt's Bees products have really gone down-hill so I can't recommend them anymore. Letting him run around in dry air will help no matter what, so you are doing good there. You can also try giving him a couple of warm baths with baking soda and letting him sit in it for 5-10 minutes. Baking soda can sometimes help. If you have an Elephant Pharm near you, you might stop in to see what they currently have. I've found them to be much more knowledgeable than Whole Foods and they can probably help you in picking a new product if it's determined that there needs to be a change in what you are using, or recommend something to help with the rash if a doctor doesn't feel it needs more serious attention. Hope this helped. Good luck!