Can Post Nasal Drip Cause Coughing

I have had sinus issues for quite some time.  I have also had post nasal drip, which I assume goes along with sinus problems.  Lately, when I take a deep breath, I need to cough.  But it's a cough that seems to be in my throat, not my chest.  Its not a deep cough or anything like that.  I'm assuming it's from all the crud in my throat.  Does that make sense?  I take Mucinex once a day.  Should I up it to 2 like the directions indicate?  They're a little pricey so I was trying to get along with one just a day.  Also, should I be drinking a lot of water?  Does that help this?  It's so annoying and it seems to get worse as I get older.  Then again, everything gets worse as you get older!!!

Hi. Does it feel as though it's more in your throat than your chest?