It could be that you are in dry air a lot - maybe even coldish dry air and it's irritating the outline. Something is irritating it. The nerve endings there would make it hurt to the touch or otherwise. If you have no other symptoms in/around nose I really would not worry , but would put vaseline on the red to soothe and heal it. If it either continues or you can't take your mind off it, go to the doctor - especially if it continues despite soothing it with a cream. Or depending on where you live, just go to a pharmacy and ask their opinion as to what you should put on it. Hope this helps
P.S. You mentioned touching your nose. We do this all day long inadvertently for a variety of reasons. We are not aware of it, and would likely say we don't often touch our noses if asked. This constant touching and unconscious pinching of the nose can either cause or worsen irritation. Again put a medicated Vaseline on it
A pimple that is deep under the surface.