I wouldn't count the 13mm out- I had more than one at that size that turned out to be mature. As for the endometrin, I would start now. Usually people do 1 or 2 supps a day- morning and night- (some Che.ck patients even do 3/day I think). I personally would start at 2 a day, but I'm kind-of a "more is more" person in the beginning. Will you be checking your P4 (and E2 if possible) during the 2ww? I think it's a good idea if your RE will agree. Usually you would do it several days before beta. Hope that helps and wishing you good luck again!