What lens do I need to do super-close-up macro shots?

Okay, simple answer: yes, you need a macro lens. The lens you are using has a 1:4 magnification at its closest focusing distance. You note that you're getting as close as possible to the subject, which is exactly right, but all lenses have a minimum focus distance. A "true" macro lens has a closer-than-normal focusing distance, allowing the objects you're photographing appear at 1:1 on the sensor.

Longer focal length macro lenses generally have similar magnification, with the primary difference being that you don't have to be as close to your subject.

You can also experiment with alternative techniques like reversal rings and extension tubes — we have a collection of information on these: What macro techniques offer an alternative to expensive optics?

If you have the budget and are really into it, you may check out the specialist Canon MP-E 65mm — see this review on the site blog. But, this is a thousand-dollar lens, and unlike macro lenses is only useful for macro, so that will depend on your level of commitment.

Generally, a dedicated macro lens will let you focus close enough that the subject appears on the sensor the same size as it is in real life; that is, a 25mm x 10mm object will take up 25mm x 10mm on the sensor. This is typically as close as a macro lens will go, though there is at least one specialist lens that magnifies up to five times.

Macro lenes of different focal lengths will all let you get 1:1 magnification in this way, the difference being that a longer lens will allow you to set up the camera further from the subject to get the same magnification, and you will also get the narrower depth of field and compressed perspective inherent in longer focal length lenses.

For extreme macro shots, a very limiting factor tends to be depth of field. To get around that limitation, you need to work with small apertures. Those imply diffraction that can be offset to some degree computationally (using deconvolution as a sharpening mechanism in raw processing software, for example). Diffraction also limits the usefulness of high pixel counts as a basis to crop from: if your image information is already smeared over several pixels, subdividing those pixels does not help all that much.

To deal with the respective small apertures, you also need light. Like, a whole lot of light. Get used to the idea of working with various kinds of flash.

Note that screw-in-between teleconverters achieve their magnification at the cost of aperture. Generally a downside because of the loss of light and bokeh, for macro photography that is an advantage because of depth of field. So consider adding a good teleconverter behind your macro lens. It will enlarge the image at the same ratio as it enlarges the diffraction patterns and consequently is as good as cropping (apart from the loss of light) while retaining a higher resolution. Basically it is the same kind of limited advantage that a higher resolution sensor would provide in the presence of significant diffraction.