Small brown spots on back/left shoulder?

So there are numerous brown spots on my left shoulder/ back and they occur once in a while. They are about the size of quarters and dimes. They are not raised. They don't itch. Just looks like colored skin dots. Light brown skin dots. I'm only 18 and so two things I do know; 1 it's not from over exposure to sun because I never take my shirt off outside (let alone out side at all since I live in AZ and it's bloody hot) and obviously not aging spots. And they don't itch. Possible skin fungus??? Because I workout every day and my back sweats but I wash it real well. Any professional advice?