When I started HRT, I immediately started to gain weight and gained 13 kg. for several months and there was no way to drop even a gram, until I started progesterone a month ago - it helped me to drop 5 kg.
I was pretty sure it will happen that way, because I've read a lot of times, that the progesterone level in many genetic women starts dropping in their 30's, which leads to excess estrogen and this slowers metabolism and therefore resulting in weight gain and very hard weight loss. Then, the progesterone intake balances the estrogen and things go back to normal.