My Answer maybe a little off topic as I am not recommending a Macro Lens.

The challenges and issues you are encountering, are not as a result of the camera equipment you mention, but more to do with the two points listed below which will help in improving your Jewellery Macro shots.

1.Aperture size.

Due to the close proximity of the Lens and subject, in order to ensure maximum depth of field and sharpness, many photographers tend to use the smallest Aperture possible. However, this is not always the best option.

The smaller the aperture, the greater the diffraction. in other words, light dispersion is greater as the aperture gets smaller and this dispersion is more noticeable when photographing extremely small objects such as Jewellery. Photographing larger areas, this diffraction is not as noticeable due to the smaller aperture often improving on sharpness by reducing lens aberrations.

A good experiment is to take a test shot with f/8 and then again with f/16 and you will notice that due to the increased diffraction, the jewellery with the f/16 has already become mushy. The light rays travelling through the aperture, have moved out of phase and started to interfere with each other and therefore, reduced the edge definition of the stones.

To get all round sharpness while using a larger aperture such as f/8, you will need to learn the image focus stacking techniques. Why would a photographer do focus stacking?

2. Lighting

A two or three light (continuos or strobe) with a light box is a fairly common lighting setup that is used for Jewellery and one that is also a fairly successful one.

When doing multiple jewellery shots, I tend to use a shiny white bathroom tile as the background. Sometimes, I place the object straight on the tile and sometimes, hang it a few inches in front of it.

I find this provides just the right amount of reflected light, plus it also provides a near perfect white background. Any grey is easily adjusted with an increase in exposure compensation.

The other most important aspect of ensuring that the image has a 3D effect is to introduce Back Flags; tiny little black cards that reflect back into the jewellery and provide the contour required for that catalogue look.