Thank you for your query at DoctorSpring.com.
Summarising your history, you are suffering from sleep apnea and using CPAP. CPAP is the treatment of choice for sleep apnea, and it can be used safely for a long term (many years). At the same time you should try to reduce weight if you are obese.
You should contact with the company/doctor who has supplied machine to you. They can give you option of different mask and you can select according to convenience.
Machine pressure titration is required according to severity of your sleep apnea based on your sleep study report.
Abnormal communication between sinus and oral cavity is known as oroantral fistula.
It is safe to use CPAP with oroantral fistula as CPAP will not increase any infection nor will it worsen it.
Definitive treatment for oroantral fistula is surgical closure, so you can plan for it. Till that you can use CPAP safely.
Hope this was helpful. Feel free to ask further queries.
Dr. Sunil Jalan, MBBS, DLO, MS (ENT), DNB (ENT).