Do you work out the same as you did several months ago? How long have you been doing your current exercise plan. I know when I upped my exercising I gained a bit or didnt' loose as much. But I think everyone goes through that area as stated before muscle weighs more then fat. So you are probably loosing body fat and gaining muslce so the pounds just aren't showing..
Anyways I'm here to support you! Don't give up! Look at the positive things you said, Your pants fit better, muscle tone, and flexibility. I remember the smallest things like when putting on my shoes wasn't such a chore because I couldn't actually bend over comfortably! Or being able to cross my legs. More then just a number on a scale is changing on our bodies.