Assuming you did 60, 70, and 80 miles a week before you got to 90 (and assuming you did at least 3-4 weeks of each), and assuming you're not running your miles too hard, you should find yourself adapting to the distance - if you're going to - by 4 to 5 weeks. What that means is that it won't be as hard to handle the volume, and you'll stop worrying about injury.
But don't expect to be faster just because you're doing more volume. In fact, you might find your first race or two to be slower! Again, this depends on the makeup of your volume. Is it all distance? Are you mixing in fartlek, hills, hill reps, or intervals? Are you racing now and then while doing your volume training?
Distance all on its own won't make you a fast racer. But it'll give you the background you need to fly once you mix in the other essential elements of training.
On the other hand, if you simply jumped to 90-100 without a proper buildup, then you're probably putting more of an adaptation stress on your body than it can handle. And you can expect to crash soon and hard.
Good luck!