On drips, mucus in throat, drool, coughing, choking. Zopiclone prescribed. Previous knee surgeries. Advise?

After having 3 ops on my knee in 11 weeks i started to get dripping down the back of my throat. This got worse and i saw my Doctor who diagnosed Post nasal drip, i have had every spray available and he said he didn't want me to have another Op as I had had these 3. I am now 3 year on and this drip is 24 hours now. I get about 2 hours sleep a night if I'm lucky as it all collects in my throat.When i eat or drink it causes too much mucus in my throat, its as if my throat feels as if food or drink is a foreign body. Im constantly wiping drool all night and sometimes wake up coughing and choking when I drop off.I try not to bother my doctor too much, he prescribed me Zopiclone just so I could get some sleep sometimes as i work full time. its a small dose and i cut into 4 and only ever take a quarter. Please help me as i am at the end of my tether now,it drives me to despair I am female. i am sorry i cannot afford £18 at this point in time. I don't think there's enough in my bank while next thursday and wouldn't want it to go overdrawn.