What is wrong with my height?

It's almost like my height never stays the same or it is all just an illusion to make me look taller >:/. I am 17 years old yet I am only 5"6 1/2. 1 week I started stretching constantly and it seemed I grew like 2 inches but now, I looked back again and I am still the same height. It's like all the new height I've gained is compressing back down to the same height again and it is annoying the crap out of me because I am trying SO HARD to get to 5"9 before puberty is over >:(. And I don't think my family has had much of a history of late growers. What's happening?