I take ferrous gluconate, which, as I understand, is less potent than some iron pills. I am currently taking 2 300g pills at supper time, and my stomach handles them fine. I am building up my iron less quickly than the other pills, but it is slowly getting there.
Another thing to watch is not to drink tea with any iron rich meal but instead to have some vitamin c with it. Tannins in tea impair iron absorption and vitamin c enhances it. They both make pretty dramatic differences to how well you absorb. Tea blocked 60% of iron, and vitamin c increased absorption by 250% or so. Well worth looking at.