hello and welcome,
the problem is due to poor oral hygiene
there is also foul odour in mouth called halitosis
due to plaque accumulation.
always brush your teeth twice daily-morning and night in vertical direction.please visit your dentist
and get a thorough check-up.get professional cleaning and root planning for your teeth.
use soft-interdental brush
and mouthwash to clean your teeth.
thick saliva may be due to more mucuos secretion in the saliva.
always clean your mouth after every food intake.
check for any decay in mouth as it can also cause bitter taste in mouth.if present,it has to be restored.
hope you get well soon.