I'm a 3C/4a natural, with hair about an inch shy of bra strap. I've NEVER taken hair vitamins.
For me, my problem wasn't getting my hair to grow - it grows. My problem was RETAINING the growth - meaning, it hard more to do with what I did to my hair, than my body's composition. I had to put away the heat, find daily use conditioners and oils that were moisturizing that didn't saturate or way down my hair. It is possible to OVER condition - which makes your hair dry and brittle. I had to get rid of the coarse brushes, and stick with simple brushes and wide teeth combs.