mrs o - you can try a steam inhalation (boiling water in a bowl - nothing in it though! - and put your head over the bowl with a teatowell over your head). that sometimes helps. otherwise, you will just have to grin and bear it!
mitchie moo - can you talk to your midwife about this? i don't think they can do a nuchal scan at 15 weeks. it's only up to 14 weeks, i think. and the guy i saw prefers to do them at 11 weeks because he says it's more accurate then, although i think that may just be him because i haven't heard anyone say they were told that. however, the dating from scans is pretty accurate, and if they are sure about the dates from the scan you had before you went away, it probably is right. one of my friends was given dates that were so late that she wouldn't actually have been pregnant when she got the positive pregnancy test according to the scans, but the dates were consistent throughout (ie the scans at what they said were 12 weeks and 20 weeks all had the right measurements for those dates, even though they were WAY out from the dates she had based on LMP, ovulation and when she got a positive test!). i don't know how this works but sometimes perhaps it just does!
but do give your midwife a call as you are right to be concerned and they definitely should be able to do that scan earlier for you.
by the way - you *can* insist on a homebirth for twins if you really want one, unless you are a particularly high risk twin pregnancy (breech positions, BP problems etc). my guess is that you may well not want that anyway, but if you do feel very strongly about it, the NCT should be able to put you in touch with someone who can help you argue your case with your health authority.