hiiii it is less likely that iron supplements cause insomnia it cause gas trouble and constipation which might be lead to insomnia but in rare case u have to find out some other reasons do u have stress problem or any psychological reason ehich is common cause of insomnia try following which is useful to get good sleep u have to follow sleep hygiene that are following fix sleep schedule and stick on it avoid daytime nap avoid alcohol avoid tea coffe soft drinks 3 hour before sleep regular exercise that makes u fatigue meditation to reduce stress light food in dinner light music while u sleep use bed only when u feel sleepy cool and calm bed room avoid any worries and dont think much in bed if they are than write it down think ab it tomorrow thank u