recommended to start SSRI, worried about weight gain.

so. earlier today i went to a gynaecologist and we talked and the recommended treatment for my PMDD was SSRI (i dont know the specifics) and others which.. i have yet to look into, but i'm worried about the weight gain

i've had a history for anorexia and a massive fear of gaining weight, i feel miserable whenever i gain in the luteal phase and i cant imagine gaining anything more than what i already am due to the side effects of SSRI. for those who have gone on SSRI's, what was your experience? generally and regarding weight gain/loss