Because estrogen stimulates endo growth (just as it stimulates proliferation of the uterine endometrium) and progesterone inhibits it, current post-hyst endo management practice guidelines often calls for the addition of a progestogen to estrogen HRT. This is intended to prevent the stimulation of the endometrial implants, reduce their proliferation and the risk of converting that endo to a cancerous state.
Many endo specialists also call for a post-op period (varying from six weeks to six months to "as long as you can stand it") without HRT, in order to encourage any remaining bits of endo not removed during surgery to shrink away. Some take that a step further and prescribe the use of a progestagen alone to directly squelch that endo growth. This may have the additional benefit of helping ease some of the transitional menopause symptoms experienced during the wait for estrogen.
Doctors are not all in agreement on post-op endo treatment, however. Some surgeons are highly indignant at any suggestion that they might not have cleared all traces of endo; others freely admit that microscopic bits of endo are virtually guaranteed to remain and require ongoing treatment. We're not going to argue with your doctor's take on the situation, other than to suggest that if your doctor insists that all endo is gone and you continue to experience post-op endo-like pains, you might want to research this part of the question further. We aren't endo specialists, but we have a few links in our bookmarks that may be useful in your researches. Use a search engine for many more resources, but search wisely: there's lots of nonsense and profiteering out there too. Endo is a long, grim battle, and it's sadly not one that seems to be over after a hyst.
Post-op estrogen deprivation treatment
In addition to progestagens, you may want to look into other measures to help with your estrogen deficit period if that is your treatment choice. You will need to work very hard on maintaining your bone density and keep an eye on your overall cardiac measures such as cholesterol and blood lipids. Both of these risk profiles see their most rapid rate of change in the year after ovarian hormones decline (and if you had pre-op therapy with hormone suppressors, that clock has already been ticking for you). Many of the symptomatic relief measures may also be helpful. In particular, use of an SSRI may be helpful if depression and hot flashes become debilitating.
It's important to bear in mind that most of the herbal/food estrogen-alternatives can totally undermine the point of going without estrogen. As a rule, the estrogenic properties of black cohosh and red clover are considered too high to be safe for use during endo suppression. Soy, which is often used as an estrogen supplement or alternative in natural perimenopause, should also be avoided in endo suppression just because it has some of the same capacity for endometrial stimulation as estrogen. Taking the adrenal precursors (DHEA, pregnenolone) is a little questionable as they can ultimately be converted to estrogen; testosterone supplementation during this period will probably also be hijacked for estrogen production, so also may not be wise. Even caffeine stimulates elevations of circulating estrogen and may be implicated in the exacerbation of endo.
Check all this with your doctor, of course—but remember the bottom line: if any of these do stimulate further endo, you are the one who suffers. And you know what that's like. Since estrogen deprivation treatment only has to go on for about six months, our feeling would be to be as conservative as possible rather than risk more endo. But you have to decide this for yourself.
Living with continuous progestogen treatment
One of the things that women with endo who choose to use a progestogen on a continuous basis to suppress their endo least like about that practice is that they more or less have to put up with a progestogen-heavy hormone imbalance. Evidence suggests, however, that employing vaginal (or, in the case of women who retained their uterus, intrauterine) delivery of a progestogen enhances its concentration in local pelvic circulation while minimizing its other systemic effects as well as the cancer risks associated with progestogen use. This is becoming a more popular strategy, with a number of available hrts suitable for this use. You can read more about them in the discussion of providing for uterine protection elsewhere on this site.