Mandy recently was diagnosed with Bordatella (even though she had a current vaccination). Our vet put her on Doxy and gave me a cough suppressant. She had started coughing/gagging suddenly on a Thursday evening (10 days after she had been kept at the vet for the day for a dental), I took her in on Friday AM, she coughed several more times on that Friday, and then only once five days later.
You really should go in to the vet--ours was concerned that Mandy might develop pneumonia as a secondary issue, thankfully she has been okay.
Sending good thoughts for Cash!