Frustration

I started making squares for my afghan. I had the right yarn and hook to match the gauge in the pattern book. Squares are supposed to be 7". First one was perfect, second one got a bit bigger, third one got a little bigger, so did the fourth, the fifth square got huge and I got frustrated. I have no idea what is wrong, and I undid all squares and put the project on hold for now. I will probably just pick one of the patterns for the whole blanket, but not right now. I have decided to seriously work on finishing some of the many started yarn projects I have laying around before I begin a new one, although there is a huge ball of pink yarn just asking to be worked with. :)