It could be "
funky hair syndrome", which can happen when you switch to natural shampoo bars from regular shampoo. The remedy is a vinegar rinse. Dilute some vinegar (apple cider is nice, I just use white) about 1:4 in water and spray it onto your hair after shampooing.
Another thing I noticed is that, as the above poster said, you need to work it through your hair. The first couple times I used it, I didn't use enough and my hair just wasn't clean. Then I made sure I rubbed it all over, and on the ends (I have very long hair). Still, a 6.5 oz bar has lasted me and hubby 4 months (together we wash about 6x per week)!
Finally, some folks have reported that their shampoo bars don't work so well in hard water. We have soft water.