Oh no, it's not just you. My kegs fall into one of three categories :
1/ I swear only 2.5 gallons out of 5 should be gone and the damn thing's sucking air already. It's magic, but dark magic.
2/ It's a beer I think is 'pretty good', but not what I'd hoped for. Of course my friends love it , but I drink from the other taps mostly. Keg takes FOREVER to kick, in an annoying way.
3/ The magical keg that manages to store 7 gallons (5 gallon capacity). I've had it happen several times. Like last New Year's Eve when the beer kicked as expected but my keg of cider seemed to last forever. My wife and I and several of our friends drank out of that keg for what seemed like forever, well past the point it should've been empty - just a 5% cider. It was like the episode of Seinfeld where Kramer and the car salesman drove the car way past the point the needle was on 'E' and kept going. Harry Potter would've been proud of that keg.