i have been in PRC since December on F type then it expired on april n extended it for a month,then

i went to Hong kong to apply for it and they gave me a month which expired in June. Im currently in Hong Kong and have been here for 5 weeks now visiting my sister and her husband. I want to go back to China, is it possible to apply for a F type in Hong Kong again, and will i be able to apply for a multiple entry 3-12months visa once i get to PRC?
I have 3 entry permits already for PRC in my passport.
Do you know agencies that can help with invitation letters and all that jazz?