Hi Melanie, there is quite a long thread about the mirena here.
I have one and I haven't encountered any problems with it at all. I have a small bleed after it was inserted and a bit of spotting over the next fortnight or so and since then I haven't had a single period.
I think it's worth a try because if it doesn't work for you it's easy to remove.
I'm still breastfeeding almost a year later so it definately hasn't intereferd with breastfeeding.