Low Ferritin - 15 years post-op

Has anybody experienced low ferritin that is 5 years out or further from surgery?

I've been taking my vits/supps daily since surgery, get blood work annually and until two years ago have not had an ongoing issue with iron until now. My last physical in 2019 it was low, they had me add additional iron, did a recheck at 90 days it was improved, reduced the iron, did a recheck at 6 months and all was fine. I stopped the additional iron at that point (my multi has iron). My 2020 physical in August it was extremely low, I had been feeling sluggish, tired and issues with dizziness and that was attributed to the low ferritin. The dr had me taking iron 2 times a day on top of the multi, recheck at 90 days and it improved slightly, she then switched to 3 times a day, another recheck 90 days later (6 months) and it was slightly improved, she had me start tapering down the iron, recheck again in 90 days (9 months) and it was low so they sent me for an endo/colonscopy. Just had a follow up with the GI who said both tests came back fine as well as biopsies and they have no answer as to why and are chalking it up to the gastric bypass. She suggested I go back to the triple iron. They are looking into the cost locally of iron infusions and stated it would be a complete out of pocket cost because insurance will not cover since I am not considered anemic since its only the ferritin that is low.

Looking to see if anybody has had a similar experience and what the reason/treatment path was they followed.

Thanks!