Leo can't go to a mortal doctor for a check-up because this will happen:

Leo: sup doc

Doctor: sit down Leo

Leo: *sits*

Doctor: now let me take your temperature

Leo: 😳 ok...

Doctor: don't worry. It won't hurt *takes Leo's temperature*

Thermometer: 200° F. {I don't care if that is not physically possible. This is Leo Valdez we are talking about}

Doctor: O_O uhhhhhh.....

Leo: I warned you

Doctor: O_O

Leo: uhhhhh...Nico?!?

Nico: *shadow travels in room* what?

Leo: *points at Doctor*

Nico: oh. *takes Leo and shadow travels back to Camp*