about Chinese visa

hi i am a medical student in china... last year i came back to pak for 1 year internship that is now over. my passport and visa both got expired. so now i have to apply for visa. invitation letter i have will be expired in march..so i wanna apply for visa now...so i wanna know d visa i will get will b upto ??? somebody told me d visa we get is for 3 months.... i just wanna confirm that.... because i wanna go bit late. thanks