Ay, I haven't had iron injections myself pero one of my mum friends got it during her pregnancy kasi super low ang iron niya, at sabi niya hindi sya masakit talaga, parang normal shot lang, quick lang and done! Pero honestly, timing and side effects talaga depends sa doctor at sa iyong body, kaya better to ask your doc directly kung gaano katagal effect niya or kung may aftereffects para prepared ka. Hope you feel better soon, iron deficiency talaga nakakadrain!