BengaLover, what's your budget? You're unlikely to get a proper macro A-mount lens (1:1) for less than €150 euro, even second hand. Your options, in and around 90mm, are pretty much limited to these:
Sony 100mm macro: link
Tamron 90 mm macro: link
Sigma 105mm macro: link
(there are older Minolta 100mm macro lenses as well)
Forget about seeing "Macro" on a lens description or name. It means nothing. If it doesn't say "1:1", it's not a macro lens.
If your budget is around €100, then your options are either macro filters, like PCPhoto said (just be sure the filter diameter is the same as the diameter of your lens). Or extension tubes, like these Kenko ones
Macro filters will degrade sharpness, but they're cheap and small. By all accounts, the very best close up filters are the Canon 500D (not to be confused with the camera of the same name) but they're the same price as extension tubes (and more limiting, since they're diameter specific), so I don't really see the point (except for some specific circumstances).
Extension tubes wil preserve sharpness, but you lose some light. They're bigger than the filters, but smaller than a dedicated macro lens. You can use them with any existing lens (even a macro, to push your magnification up), and good ones will even preserve auto focus (although, for macro, you'll usually be using manual focus anyway). I wouldn't bother with anything other than the Kenko ones above.
I have all three (filters, tubes and lens). I never use the filters any more (bought them years ago), and I only use the tubes with the macro lens to give better than 1:1 magnification. I use the lens on it's own a lot.
So if you want the best 1:1 macro ability, go with one of the lenses above.
If you're budget is tight, and you want to preserve quality, go with the extension tubes.
If your budget is very tight, you don't really care about quality, and just want to mess around at getting very close to small things, go with the filters.