My hair WONT grow at all?

Last time i had my hair cut was december, and i know what your all going to say; your all gonna burst into the whole 'have your ends trimmed every so often' song. but i've asked my hairdresser and she said it doesnt help the growth; it just make your hair tidier, neater and better quality. im not bothered about any of that, ill care about it when i have long hair, but my hairs stuck. its been growing and then it just gave up when it reached about the end of my shoulder, and its not that my hair wont grow longer, becuase ive had it much longer before. also another tip i read online was that if you keep your hair up in a bun for about 1-2 months and dont take it out (apart from when your washing it+ sleeping) when you eventually give up your hair seems to have grown loads; becuase youve not watched it grow, i tried that and i see no difference; so help!