It can take a long time to up your hemoglobin to return to normal levels through food alone, depending on your iron saturation. Many people should consider supplementing ferrous sulfate with vitamin C, checking every month or two at the lab on the results.
I’ve read that the body absorbs non heme iron pretty well when it’s deficient, and is able to block excess absorption when it has enough. But does not block additional absorption of heme iron regardless of iron levels.
If you do want to boost absorption, broccoli has vitamin c and probably other benefits.