It’s very common for locks to seem like they are only getting thicker without growing longer for the first 12-18 months. Rest assured that locks do not change the rate by which your hair grows.
At first it may seem like your hair isn’t growing, because the starting and maturation process can make some sets of locks shrink up to lengths shorter than the individual hairs. Because of this, it can take a while for your locks to grow back down to the “original length” of the hair your started with.
But don’t worry! You’ll notice growth in due time! It took me about two years to notice growth in my current set of locks, and they seem to be gaining length rapidly now.