I'm sorry you are dealing with this.
I started taking Megace over the summer for endometrial cancer, which isn't the same as fibroids (thank God for you!) but I thought I'd chime in about progesterone in case it may help you.
I take 40mg x 4 a day (every 6 hours). As far as I know, it's considered the max. dose doctors will prescribe. I was warned about weight gain (I lost all my weight since I started the meds so that didn't apply to me, gaining weight is the last thing I needed), have to be active due to the blood clot risk (which also helped with my weight loss), and of moodiness/depression/lack of sex drive.
I can honestly say that the lack of sex drive is the only thing that applied to me (I was already a little moody to begin with so who can say if it's the meds lol). I am not sure if it's the meds causing the lack of sex drive or the stern warning from my OB/GYN to make sure I don't get pregnant while taking the progesterone as it causes birth defects. So between the sadness of the cancer and the fear of God not to get pregnant (which I 99.9% can't anyways due to the cancer tissue anyways), I wasn't and am not rearing to go at all. Definitely affected whatever controls the urge but also stopped the bleeding which halted activities anyways. But the meds definitely have something to do with it I think.
I'm sorry if this is TMI but anything I can do to pay it forward with my experience on these meds I'd be happy to. There aren't a whole lot of young women (I'm 37) out there being treated with these meds to get a whole lot of feedback online or otherwise.
Good luck with your fibroids, I hope you get some relief soon.