I am 20 weeks pregnant and I can still fit into my regular jeans. It is a little snug, but I haven't gotten so big that I can't wear any of my regular clothes. But every person is different of course...but most of the growing is done in the last trimester, which you are about 10-12 weeks away from.
Honestly it depends but in 4 weeks you probably aren't going to be much bigger. I didn't have a dramatic change until I was about 6 months once I hit that I started getting much bigger much quicker.