@Krysta74 yep you need some sort of progesterone support after transfer. I know one clinic I used to go to didn't believe in it for FET.
As you are transferring today, I would ask for pregnyl, it's not progesterone. But will fool your body into thinking you are pregnant (by producing hcg) so then your body will produce its own progesterone.
The only down side is you can't poas as it will give you a false positive. I took it the day before transfer, 3 and 6 days post so I reckon you could take one today then follow that, but ask the nurses.
Otherwise they can give you crinone or pessaries. They will still up your progesterone, it will just take a cpl of days to build up. But ladies who have upped their dose in pregnancy see results quickly so there is no reason why you can't start now.
Pessaries/pregnyl/crinone won't interact badly with the clexane and steroids. I am on high dose steroids and clexane as well as others and I'm fine.
Good luck xxx