You need a belly band!!! Get one!!! They are made by the angels themselves.
I can still wear my jeans and i'm huge for 23 weeks!!
Their nice and cheap, and it means basically all the pants that you can't do up anymore, you can still wear. And they give your tummy support.
PLUS, you can use them as a bra to sleep in. Very very comfy.
Buy one, you won't regret it. I'm wearing mine now and still congratulating myself on getting one. Lol