Could it be twins.

This is my first pregnancy. I'm due a scan next week so not got too long to wait but I'm thinking it could be twins... My husband was supposed to be a twin but the other one didn't develop ... I've felt so sick from week 6 until recently (although not BEEN sick very much) my tummy looks and feels huge and I've put on 14lb despite eating in moderation...has anyone had twins. When did you realise/find out ... ???