I've started having night sweats, with an onset of one year ago. i wake up to drenched sheets but i'm not overheated. i don't sweat during the day.

Fever?: Assuming the room is not overly warm, and not using unnecessarily heavy covers, this is something to see a doctor about. True night sweats occur because of fever that drops during the night. See a doctor, and for a week before your appointment, take your temperature (and write down the results) 3 times a day: when you awake in the morning, 4-6 pm, and at bedtime. Also record the nights you sweat.