I agree that it sounds like they're not getting clean. Switch to a non-homemade detergent and use some bleach. I can't tell you how many times I've talked to someone who was having rashes when using homemade detergent on diapers. It's a bummer because I love the idea of homemade detergent also. I am currently using it on my kids' clothes, but it just doesn't cut it on the diapers.
Rebecca, married to J (2007), DD1 Anna (11/09) and DD2 Ada born at home 7/12 DS Henry born at home 3/14