Wow.....someone with the same problem I have !! I used to think I was crazy but I swear my hair has been the same length for years.
First off, trimming it makes no difference how much it grows,,,the new growth has nothing to do with the ends. This is a common fallacy. What people mean is by trimming the ends you are conrolling the amount of breakage on the bottom, so the split ends do not travel further up your hair causing more breakage...but this has nothing to do with the hair growing from the roots.
I suspect it's really just an illusion your hair is not growing.. Everyones hair grows. Probably it's splitting at the bottom just as fast as it grows. Therefore it is appearing to be at a standstill. Start by conditioning weekly or as much as you can stand concentrating on the ends. This has helped me a little.
I would love to hear any other replies...I have tried vitamins, scalp stimulating. etc.... but honestly I think the rate of hair growth is genetic. I totally sympathize !