I'm not too worried as I'm extremely well-monitored by the hospital here as I had a lot of problems with my first pregnancy. They took great care of me and baby then, and even though this pregnancy is so far looking much better, they're keeping a very careful eye on me to spot any problems well in advance.
I'm due to see both midwife and obstetrician on Monday so will be mentioning it then anyway. They'll be doing urine, BP, bloods, scan as routine, they always do (they're thorough!) and so far all bloods and urine have been fine.
Thanks for your advice though. I just hope it doesn't itch like this for the next 18 weeks! Cold showers are definitely worth a try.