Am I getting shorter? (Please read full question)?

[Tatortot]

I know it sounds stupid, but I'm either 5'9" or 5'6" and a half.That's a wide range, I'm aware, but I had my dad measure me a couple months ago and I was 5'9" and I had him measure me today and I'm 5'6". I don't drink coffee, or tea because I don't really like the flavor. I'm on the computer a lot (twitter addiction, haha) so I'm 'hunched' over a lot. Is it possible I'm shrinking, well not shrinking but getting shorter? I stand up straight and very still when my dad measures me so I'm quite positive it's not the measuring that's wrong. I'm perfectly ok with getting shorter, I've always wanted to be a bit shorter just because I can't find proper jeans that aren't a lot of money for my height. Also I can't find proper shoes that are cute without spending loads of money.

Anyways, if you can help me out, thanks (:

[Lulu]

No you cannot lose 3" at all. Stand against the wall with your heels touching the wall and place a piece of card on your head,get someone to measure where the card comes to and then mark the wall. Now measure from the mark to the floor. That is your correct height...............