Why do some mantras calm me instantly while others don’t seem to work?

My name is Aditya Ramesh. I was born at 6:15 AM on the 9th of February 1997 in Chennai. Incidentally, the sun was rising very brightly. I have been playing with different mantras: "Om Namah Shivaya," "Om Mani Padme Hum," and "Gayatri Mantra". There are occasions when, for several minutes, I repeat a mantra silently and it cleans my mind of the heaviness of anxiety, that is, the anxiety disappears and the heart slows down. These are also times when I don't feel any chanting impact at all. I sometimes wonder if it depends on the energy of my body, my mood, or how I chant. Could astrology be the reason as to why some mantras work for me and not others? And what would be the way to keep getting the benefits?