lydialovely,
natural FET means going natural letting your body ovulate naturally without the use of any drugs. Once ovulation is detected, ET is schedule about 3 days after, and we also start progesterone inserts then. It's relatively simple and stress-free on our bodies, but cycle could be abandoned sometimes when our body doesn't respond the right way, and natural FET needs more monitoring as timing is crucial.
Medicated FET means taking estrogen to build up our lining and dominant follicle till body is forced to ovulate. This is a sure cycle. I tried both and definitely prefer natural fet simply because I don't like to introduce drugs unnecessarily. But now that I tried both and failed, my next cycle I will be trying a stimulated fet cycle. injections again...sigh..
By the way, I didn't have any side effects when I was on progynova, which is an estrogen drug. Could you be feeling stressed? Maybe other sisters can comment more.