Those are really low scores. Glad you are getting the IV. In a case like yours, it is needed. On an onging basis, you are probably going to have to figure out how much iron you need to supplement a day. The only way to do so is by trial and error, with lab tests to corroborate how you are doing.
Do not take the iron in a multivitamin. This does not help it be absorbed better. In fact, the opposite is true. Things like calcium in your multi will interfere with iron absorption. GIs are worried about iron supplements irritating the gut, but whether iron will irritate the gut or not has nothing to do with whether it is or isn't in a multivitamin.
I'd be happy to email you an article from a medical journal that discusses how Crohn's patients should receive iron supplementation.
The best way to take iron is straight. My daughter takes 25 mg of iron a day with orange juice...the vitamin C helps the iron be absorbed. She does not eat food when she takes the iron, because food interferes with absorption of iron. She also does not take iron any sooner than two hours after taking another med, vitamin or food, or one hour before eating. Because even food, meds, or vitamins (like calcium) taken less two hours earlier could interfere with iron absorption.
My daughter has done systematic trial and error of lab tests to figure out how much iron she needs on a daily basis. She tried taking the 25 mg 5 out of 7 days, or every other day, etc. The only thing that works to keep her iron up is taking it every day. 25 mg is a low dose, but it does build up.
The duodenum is where iron is absorbed by the body, so if you had problems in that area, then you might have more trouble absorbing iron.
Daughter (20) Dx'd Crohn's 3/06. Misdiagnosed for two years, including by top pediatric Crohn's specialist as stress and needing more fiber but landed in hospital in 3/06 with cramps, vomiting, stricture. Now in remission with Entocort 3 mg (one pill), SCD multivit, yogurt, vit D3 1800IU, 900+ mg calcium, 50 mg B complex vit, 25 mg iron. Off SCD diet but wheat was iffy so back on SCD modified to include potatos and rice.