Are supplements enough?

Back in January, my ferritin levels were at 23 ug, so not exactly anemic, but definitely too low. not surprising because i was feeling lower energy than normal. ive been taking 28 mg iron supplements almost every day and i dont know when i should get my iron checked again or how long it will take for it to go back to normal, but i am worried that im not getting enough iron in my diet even with the supplements. is there a recommended dosage of iron im supposed to take?