Most of us endo ladies have a tilted back uterus (quite normal as it is meant to be able to flop one way and the other... but sometimes gets stuck back with adhesion, very very common from endo but you don't need endo to have a tilted uterus- just remember that when you are scanned you should be having internal ultra-sounds not over the tummy ones, so that your insides can be seen more easily.)
Thick endometrium can be caused by a similar condition to endo, called Adenomyoisis, which grows in the walls of the uterus and makes them thicker, so it might be that at the top of your womb that you can feel.
One of the ladies on the forum set up the adeno information website
Well worth looking at her website just in case, the good knews is that there is actually a cure for adeno - bit drastic, but a hysterectomy will rid you of adeno when the time comes.
symptoms are much the same as for endo, but the cells are slightly different, hence it has a different name. From what you are describing, it sounds quite a likely possibility, certainly one to be looking in to.