Coughing problem. Is this in my saliva?

What is this in my saliva ? I'm having frequent spitting problem from last 4 weeks i get urge to clear my throat and in morning i wake up with my throat filled with phelgm or saliva which i have to clear . I spit more after drinking or eating something . I consulted a ent on practo he told it's sinusitis and post nasal drip , he gave my medication for five days and recommended steam inhalation my condition improves little in day time but in morning i still wake up with phelgm or saliva like this in my  throat which i have to clear . I don't have any fever nose blockage chills or breathing difficulty . After my condition not improved fully he told me to consult respiratory physician beacuse of this black or brown spek in my saliva . Most of time i spit clear saliva or clear white phelgm but some time this black speks are coming .