Lunar calendar 1990 is indeed a leap month and a leap month. If your mother says that you were born in a leap month, the Gregorian calendar birthday should be June 28th. But it is also mentioned that "Longyang Day" should be June 6, and the Gregorian calendar is July 27.
As for what the fortune teller said, it must be because your mother told him about Longyang Day.
My opinion: can you ask your mother if she was born in the sun again, and the rest will be easy for you!