The perennial herbs that really need to be divided are those that produce multiple small plants--chives, mint, lemon balm, etc. Sage and oregano are really small bushes, and are generally one plant, so no division is really needed. It's possible yours just need pruning, or some compost or fertilizer added, since they've depleted where they're planted. Now, the other option is if your oregano has divided itself by layering it's own stems that fell into the dirt and rooted, producing additional plants around the main.

Mediterranean herbs do not generally need any fertilizer and in fact will resent rich soil. Sage is one of those. Oregano also does fine with lean soil so I would not think that fertilizer is an issue for either.

Oregano can crowd itself so moving some of it elsewhere or giving away a pot full to a friend, may refresh it.

And some plants like sage are not overly long-lived. It is vigorous when young and not when it gets more aged. I would suggest adding a small, young sage plant every 3 or 4 years to keep up the production. I locate sage plants in a number of locations so I always have some young vital plants as well as more aged plants that are not so vigorous.

FataMorgana