Adequate "size" depends a lot at what level you are playing and you don't tell us that. A meaningful answer requires that information. That said -- how are your passing and (box) kicking skills? Were you at a senior or even a U16 level, your size screams scumhalf. Edit: Then I'd say you are probably in the backs. A little too small for hooker -- the props would have trouble binding too you. Flanker is a possibility, but you are a little small for a forward -- even a loose one. So -- tf your skills are up to it, scrumhalf or flyhalf. Winger is also a possibility.
I'd say hooker or scumhalf!!
I'm 5'3... apparently we make good hookers:)