An Occasional Voice Problem ?

An occasional voice problem ?
Okay, to start off with. The problem I have is I have got a severe nose block which is permanent. That stays 12 months. I’m pretty used to it now. I reckon this nose block is due to the the place I live in. England. It derives from bad pollution and dust. If I go abroad to countries like Bangladesh or other hot asian countries, I find it slightly more comfortable.
But my main problem is, with a nose block, every time i blow my nose and not to mention I also got a permanent cough. No Asthma whatsoever. So every time I cough or get rid of my mucus either through blowing my nose or through phlegm, I realize my voice gets very weak. I find it very very difficult to project my voice. It goes so weak. It’s unimaginable.
I’ve already taken plenty of medication. From the likes of nasal spray, pills, tablets, Inhalers so forth so on. But none of them seem to work for my permanent mucus disorder. My last resort is a nose operation I’m gonna decide to do very soon. But before that, can someone tell me how I can improve the richness and the sound and power of my voice. Because anytime soon, my blocked nose or cough is not going to vanish because the mediction has not work. So in the mean time, can someone advise and give me tips on how I can maintain my normal voice even If I blow my noise or clear out any mucus.
And also, it will be extremely helpful if someone tells me what the nasal passage has got to do anything with the production of voice. Because that seems to be the main issue here.
Thanks in advanced.