How can I stand up for myself?

At work I share an office with two other middle aged men and a lady who has only recently started. I'm good friends with the guys but I feel really down as they wind me up all the time and I can't stand up for myself. For example they sometimes don't speak to me or ignore me when I ask them a question. Also they are sometimes chatting and when I join in they say "Who's given you permission to talk?". One of them often says "shh" when I say something. I'm always helping them when they have queries and I'm the one who makes most of the drinks during the day. I'm down as I ume that as I've always been like this I'm not likely to change. I do sometimes say something but they don't seem to take me seriously. Can anyone give me some advice please?