4 of the 6 shots were shot at 18mm. If you were at minimum focus distance with these shots, at 18mm you will have far less magnification of the subject than shooting from the same distance and using the maximum focal length of this lens, which is 55mm. Your first jalapeño shot was taken at 18mm, and includes a lot of the plant and background. The next two were taken at 48mm and fill the frame with the pepper. Not all shots need to fill the frame with a small object, but that is what I understand you are attempting to do, and is generally considered to be the point of closeup photography. When using a zoom lens choosing a focal length setting is as crucial to framing an object as is focus distance. If you are looking to fill the frame with a small object, then choosing a longer focal length will help you do that, unless you are using something else to decrease minimum focusing distance.
If you aren't happy with the ISO setting in the closeup mode, you can change it by going into the menu and manually choosing the ISO you desire. The camera will then choose exposure settings at that ISO. I'm sure that your camera is currently in auto ISO mode. If you manually set the ISO, it will stay at that setting unless you switch to Auto Mode on the mode dial. It should then switch back to your selected ISO when you switch out of Auto Mode to any of the modes, like Aperture preferred, or closeup.
Regardless of the mode you are in, you need to pay attention to the exposure settings you are getting and make changes as necessary. You should find a mode that works best for you, your shooting style and what you are shooting. I use manual with auto ISO for most of my bird shooting. That works well for me, but I do have to watch what is happening with the ISO and sometimes change the shutter speed, or perhaps aperture. When I am shooting macro, I use full manual for everything when I'm using flash. If I switch to an available light macro shot, I normally switch to aperture preferred with manual ISO. These modes work for me. They may not work well for you.