My brother had severe polyps and went through exactly the same steps you have. And afterward was told to just continue the nasal wash and prescription sprays. That's about all that can be suggested, and it sounds like you're doing just that. It's now been two years since his surgery and he still has no sign of the polyps regrowing (and his were BAD...the ENT said they were the largest he's ever seen! Of course, that's partially my brother's own fault for letting his symptoms go on for so long untreated.)
Yes, it's also okay that you don't need another checkup for 3 to 6 months.
It seems that you're doing everything possible and everythign right. Don't worry, you'll be fine.