How annoying and disappointing. You seem to be doing everything you should be! I do know that the iron in supplements isn't very well absorbed even WITH vit C so I suppose my only suggestion would be keep up a diet high in leafy green veg and red meat and see how that goes. Good luck.
I took Fluroxide (sp?), I was really sick with dd3 and midwife advised me that it would be much easier on my stomach than tablets. It tastes like shite, but worked, my levels had gone quite low late on in pregnancy but it wasn't picked up on. I saw results quite quickly.
Floradix is much the best thing to take-you can get it in Holland&Barratt. I was given a prescription for iron tablets too but they were awful. I can't recommend Floradix enough-it even tastes quite nice!
Go back to your GP. You don't have to have ferrous sulphate, there are (pricier) alternatives such as ferrous gluconate, which is far better tolerated. You don't have to put up with feeling bad and awful side effects.
I had the same experience as you - suffered with the iron for a month and my numbers didnt go up, and I still felt tired, I have been on a vit B complex for a week now and feel so much better, hopefully next set of bloods will show a difference too.
I've been taking the spatone, with a monster 1000mg Vit C tablet at the same time (any excess Vit C just gets flushed out), and when I had my 28 week bloods the consultant was pleased that the levels were holding up - which is apparently fairly unusual with twins. They don't seem to cause any of the problems with tablets with me. They are expensive, but Tescos usually do 3 for 2 on them, if you can't get them prescribed.