Hi Fedup, good luck low iron sucks! I have very very heavy periods and with that have continuously low iron so will dump a load of generic advice I have researched over a couple fo years, sorry in advance (and obvs take doctors' advice first!)
Firstly don't even bother trying/thinking about getting more in your diet, even iron-rich foods hardly have enough unless you eat liver or black pudding especially if you are already low. Supplement away.
Secondly, it is possible you have an absorption issue, but as you have a sleeve (which unlike the bypass don't skip the first bit of the intestines) I think it's much more likely that it's just the small amount of food combined with what sounds to me like way too little supplementation and possibly safe but low levels pre-surgery (NOT a doctor).
Things that help the absorption of iron: vitamin C, things that obstruct it, Calcium and caffeine. So when you supplement make sure it is not with caffeine or other supplements like calcium or magnesium, it should ideally be along with either fruit juice or a vitamin c pill or gummy. Multivitamins with iron combined often dont help as teh iron is just blocked. If your diet is anything like mine post-surgery... there was a lot of dairy! Also... im pretty sure i used to get most of my iron from chocolate, white bread and sugary cereal beofre surgery.
I also paid privately in the Uk so might have a slightly different perspective to those from the USA above. They won't just do infusions here the way alot of people have been discussing above, they arent covered privately with the cost of surgery, and NHS will supplement first and you need to be ILL. I used Nuffield so your package may differ, but the surgery cost covered the dietician for that year, but not costs from them, so they can ask your GP to prescribe stuff but cant directly. Hopefully its all sorted now but in teh future I would not rely on them to get stuff actioned, get on the phone to the GP get an appointment and get them to prescribe you what the dietitian recommended. I just demanded a repeat long-term prescription of iron pills.
As I say my deficiency is chronic (I prefer iron to birth control at the moment) but I have been on 305mg Ferrous Fumarate every other day for a couple of years, you can also ask for the more expensive ferrous compound if that gives you issues. Maybe try floradix if you can stomach it 🤢. But anything below 100mg or so a day just cant combat the deficiency.
I would up my dosage, check when/the combination of supplements, and keep on chugging, iron deficiency is really normal and very fixable and not down to your diet.