Why does my freeview have poor signal?

Basically, my free view only gets bbc1 bbc2 bbc 24 news, cbbc, red on. Sometimes if i'm lucky i'll get dave, e4+1 and some others but not fiver 1t4 or bbc4 :( But even the some channels that i get- the screen freezes and then sometimes it says no signal and the screen goes blanc. I love xfactor and i can't watch xfator as my 5 channels with out freeview have awful quality. I'm fed up of having no tv. Please some one help me!!