If you wash your hair with shampoo more than twice a week, you are definitely over-shampooing your 4b/4c hair. At least this is what I have learned from experience. I used to wash my hair with shampoo at least three times a week. Now I only use a clarifying, sulfate free shampoo once a month, or as needed. Just because a shampoo is made with all natural products that does not mean that you should use it everyday.
4b/4c hair is the most fragile hair type. The hair patterns make it really hard for oil to travel up the hair shaft. This type of hair needs to be moisturized and conditioned very often to keep it soft and healthy. Most hair experts recommend shampooing African American hair 1-2 times per week unless you have a hair condition that requires you to shampoo your hair more often.
4b/4c hair should be conditioned daily. The hair should be rinsed with warm water, washed with a good moisture based conditioner, then the hair should be rinsed again with clear, cool water. This process will make the hair easy to manage. A leave-in conditioner should be used after each wash, followed by a good oil to seal the moisture in your hair.