just seen that you're in newport - have you tried bon marche? they have some quite oldish clothes, but i managed to find some good tops in there before (and i was larger than 18 at the time). Also Newport has an Evans doesn't it? size 18 isn't that bad tbh and you should be able to find clothes that size pretty much everywhere, but watch the trendy shops as their sizes are a lot less generous. E-bay is a great idea but if you need it for this weekend, i'd head into town. plus there's loads of charity shops in newport (i used to work there so my lunchtimes usually consisted of a wander around them - and some of the stalls in the market have some quite nice tops). you shouldn't really be struggling to find clothes to fit. most important is to get a good fitting bra - can make an outfit - which reminds me, i must go to m&s for a measure up.... good luck x