I am using a saline and steroid nasal rinse. can this cause dry mouth?

Not usually: This is unusual. Sometimes nasal steroids can cause thrush (oral candidiasis) which can cause dry mouth. Have your PCP examine your mouth for any signs of thrush

Some dryness expecte: Steroids can cause some nasal dryness but using the saline will help remoisturize the nasal membranes.

Definitely, yes: The steroid nasal rinse form affects only local areas but if used excessively, side effects may include: headache, dry mouth, and dry nose.