What are the common ingredients? What is the pH of your water source?
If you are used to shampoo with sodium lauryl sulfate and switch to one without it, you may experience "buildup" at first. SLS is very good at stripping oils, but that also means that your hair will produce more oils to compensate. There is an adjustment period.
Hard water (that with a basic pH) also hampers some natural shampoos. Using a water softener can help, or you can try rinsing with an apple cider vinegar solution to clarify the scalp a bit. I didn't have any issues with my hair routine until I moved to a place with hard water!