I'm no expert, so I'll be interested to read what others chime in on this.
For myself though, I'm just experiencing the same for the first time ever. I have only lost a couple of pounds in the last 3 months, but suddenly last week I noticed that I was now having to tighten my belt to the third notch, when I bought it 2 1/2 months ago it was at the first. So I thought it was just that it was a new belt, so it must have stretched. Then I noticed this week (when I didn't have a belt on my jeans) that my jeans were suddenly loose as well. For me it really seems to be affecting my waist area the most, which is a bit strange as that's probably where I have the least to lose.
Anyhow, I'll take it!
Congrats on your measurement loss and keep up the good work!