I want to ask, what is my 1999.4.20 constellation? Lunar birthday?

It can be seen from the two screenshots that you are a Gemini, and your date of birth is May +0, 265438 to June +0, 265438. You are the third house of the zodiac, representing impetuousness and communication.

Gemini people like change. Spring is manifested in Gemini's personality, which is characterized by fickle thinking, unrestrained, and endless curiosity about everything outside. It can be said that Gemini is an alert, active and uneasy constellation.