I use a CPAP machine with nasal pillows. I have a sinus infection along with significant post nasal drip. Should I stop CPAP temporarily?

Use face mask. If you can't breathe easily with nasal pillows, stopping CPAP will likely make you life more miserable because you are now dealing with not just a sinus infection and post nasal drip, but also a lack of sleep and less oxygenation to the brain. If possible, use a face mask for your CPAP, so you can mouth- breathe at night.