call me a pessimist, but i don't think that it can healthily (is that even a word??) happen in only 3-4 months.... i mean even if you practically od on every vitamin, topical growth aid and miracle potion out there, the goal itself is unrealistic...
may is ask if there's a particular reason that you want to hit this goal pretty much yesterday??
i advocate time/patience, and that's really what it's going to take... until then, i'd recommend staying in the weaves while practicing healthy haircare, if that length is what you're craving... i don't know what your current hair practices are, so maybe if you reveal that, that'll help with the general growth advice you'll receive...