Are you using the identical gear you used a couple of years ago? If you've replaced some things, or added some things, that will change the weight.

I find, from year to year, that I tend to add things, "because it's only half an ounce (or two ounces, or whatever.)" I'll convince myself that the stove that used to live in my food bag needs its own stuff sack, or that having an extra collapsible water bottle could come in handy someday. A monocular is fun to take, or a set of toenail clippers is handy, or maybe I decide I should increase the number of matches or ibuprofen or safety pins I take - and the next thing I know, my pack is a pound heavier than it used to be. So, I get ruthless and ferret out all the culprits and eliminate them. And then, a couple of years later, repeat the cycle.

And then there's the obvious: are you using the same set of scales you used two years ago? (Ask any handyman why you don't measure with your tape, and use your buddy's tape to mark the board.)