Could be many things.
it can be Rash, or Insect bite, Can be from rubbing or pressure.
See if it grows. or shrinks.
If its still there after few days go check out doctor.
Don't worry though. there are many things that cause spots like that. even fungal infections like you said.
But if it persists go see a doctor. and they can tell you what it is. and then you can either take there meds or cure it with natural treatments.