Hi, I am also 5'4 and have always yo-yo'ed. Im 30 yrs old now and wiegh 134, but in high school I was 145, then later I was 140 etc.etc.etc. I was even 200 when i delivered my first child.
Heres the key in stopping the yo though.
Lots of water, no suger hence candy,ice cream, no processed food(anything from the freezer or take out) LOTS of fruits and veggies, and whatever exercise floats your boat.
Sounds like it ***** but it really isnt that bad. :)
Dont get me wrong, I do indulge in the occasional few,couple of small bags of chips or combos once and awhile LOL (wink)