Hello Lybrate user, yellowish discolouration of teeth is due to improper brushing, so start brushing twice daily in proper way. Also I think you need to have scaling and polishing of your teeth, that means cleaning of teeth with the help of ultrasonic instrument. This will remove the hard deposits over you teeth. Also foul smell is due to infection
so a course of antibiotic will help. Visit your nearby dentist
for scaling and polishing. As far
as salivation is concerned, you must be mouth breather, i.e your mouth must be open during your sleep. Hope this helps.