If the Tamron lens is a throughout macro, then you might want to but 55-250mm IS. But definitely keep the tamron lens with you. Don’t sell it.
If you do, i might be interested in a cheap macro lens :))

I haven’t used 18-200mm. More range a lens has, generally, the IQ deteriorates, but not always. I am totally happy with 55-250mm. I am more than happy in fact. :)

If you don’t want the reach of 250mm (or beyond), and don’t want to change lenses either, you can buy 18-200mm.

50mm 1.8 is a very good lens. I have used it a few times, and it’s worth every $.
Haven’t used any macro lenses enough to comment on them.

Tamron 100 to 300 mm is Macro only with no IS, aperture is 5 to 6.3, so not fast either. The lens is a bit on the heavy side. IQ is great though, better than 28 to 80mm.

I do like the 55 to 250 for its IS and a decent aperture range. I also read somewhere that 18 to 200′s IQ is a compromise for convenience, as More zoom that a lens has, the less will be its quality.

Have you tried a prime lens? 50mm 1.8 ? or the 50mm 2.5 macro?

Is Tamron 100-300mm a macro lens? What is the aperture? Can you use it without macro mode? If you can use it as normal lens, you don’t need to upgrade to 55-250mm IS.
300mm is a decent reach, but maybe (just maybe) 55-250mm will provide better image quality, and yes, IS is helpful.

Deciding what lens to buy basically boils down to what you want to photograph. If you answer that question clearly, buying the lens becomes very easy.