Don't know what shutter speed you are using, what kind of results do you get when you shoot in full "auto" mode? (JUST for the sake of taking shutter speed and other settings that might be incorrect out of the equation.)
Let's get the shot clear and in focus, then worry about the exposure settings.
I take tons of photos at night without using either a tripod or monopod.
To me, your photos look blurred, and out of focus, which might be two different issues... Your focus might not be correct, and / or you might be moving the camera slightly while the shutter is open. Please make sure that both your camera and your lens are set to the autofocus mode.
A tripod would probably help, but this might not be your problem either, or all of it.
You would be surprised how many people I see taking photographs who do not even know how to properly hold a camera when shooting...
Many people hold a camera with their elbows outward, flapping like wings on a wounded duck - WRONG!!!!
Try supporting the camera with your left hand under the camera in the palm of your hand, your left arm and elbow tucked into your body. You can hold the camera, or both camera and lens that way, and your arm is tucked into your body for support.
Your right hand (trigger finger) is positioned with your finger on the shutter, then you also tuck that arm and elbow into your body.
Spread your legs slightly until you feel stable, breathe deeply, then settle down, depress the shutter button halfway down until the AF does it's thing (a Nikon will tell you with a little green light inside the viewfinder), then take the shot.
If you need more support like a tripod or monopod and don't have one, you can also lean against a wall or something for a little extra stability.
Try this and see how it works for you...