How To Treat Chest Congestion Inspite Of Taking Guaifenesin?

I quit smoking 4 1/2 months ago and have had intermittent chest congestion.I have used guifenesin to thin the mucus but want to know if there are prescription medicines better than that. Have also used prednisone in emergency situations but don't want to get involved with that. I have asthma and have used albuterol with doctors care but it does not help with the congestion which can be scary at times.