Iron levels.

I'm anaemic and my midwife has said my iron levels are at 95 when they should be 120. I've been taking iron tablets for about 2-3 weeks now. Had my bloods taken today at my 34 week appointment but was warned that if my iron level hasn't gone up then I'll have to be sent to hospital to have a iv iron infusion? Can anyone advise me on this please? What does it involve? Thanks.