Cough Suppressant?

For the last two weeks I've had this nasty cough. I got it from my dh. Last night, and the night before, I've only been able to sleep 3-4 hours, with this cough keeping me up. I have no other symptoms of a cold at all - just the post nasal drip that causes me to cough, especially when I lay down to sleep.

What has worked for you? I have high blood pressure, so I can't take everything that's on the market. Thanks in advance for your help.

PS My doctor has given me a prescription that does nothing at all.