Toddler is constipated!

My daughter is almost 14 months and at her 12 month check up we found out she is slightly anemic so we've been giving her NovaFerrum (liquid iron supplement) every day but now she barely poops and when she forces one out it's practically like a little rock in her diaper 😭 I feel so bad and I'm not sure how to help her have normal poops again. She's still breastfeeding often and is very picky with what solid foods she eats. Any advice? Have any of your toddlers had this same issue?