Ugh, I feel your pain. I spend thousands out-of-pocket on medical and dental care every year, and I have good insurance! And it's not like I have something horrible, like cancer -- just a lot of miscellaneous stuff.
Anyway, I tend to do everything at the time the doctor recommends it. It just scares me to do otherwise. You can look into Care Credit, which is a 0% interest credit card for these kinds of issue. It's a reputable company which has been around for a long time.
Definitely max out your pre-tax flexible spending account.