Assuming you have the 50-200 (55-200 does not exist) which has a 1:4 maximum magnification, it allows you to take a picture of a fly that's e.g. 1cm in real life; on the sensor, this fly will be 2.5mm or roughly 10% of the width of the image. Using a macro lens, this same fly will be 1cm on the sensor as a real macro lens has a 1:1 magnification.
There are different macro lenses; in the current Pentax line up 35mm, 50mm and 100mm. The difference is that to achieve 1:1 magnification, you have to be closer to the subject when using a 35mm lens (14cm for DA35Ltd macro) than when using a 100mm lens (30cm for DFA100WR). There are some advantages in the longer lens
- you don't chase your subject away when getting really close
- less chance of the camera being between the subject and the light source
- a little 'safer' if your subjects are of the aggressive types
If the only lens that you have is indeed the 50-200 (and no 18-55 or similar), I would first look at options to get something 'standard'
DA18-55WR (or similar like Pentax 17-70 / Tamron 17-50) or DA-L35/2.4 as a 'standard' lens.
The kit lens already gives 1:3 (at 25cm) versus 1:4 for the 55-200 (at about a meter).
The cheaper ways into macro include extension tubes and reverse mounting a lens; there are more knowledgeable people than me who can advise on this. You can also add a Raynox adapter (DCR150, reasonably cheap) to the 50-200 to obtain macro functionality (not sure if you can achieve 1:1, but probably quite close to that). Macro work often is manual focus work, so you can also look at some older (second hand) macro lenses as well.