Hi Rohit,
The sun's total over all brightness changes a very, very small amount - about 0.1% over the course of the eleven solar cycle. That is such a small change it is very hard to measure, but we have special instruments in space that can do it.
See https://www.nasa.gov/topi...lory_irradiance.html

Over much longe time scales - billions of years, we think it changes quite a bit. Over the last 4.5 billion years we thing the sun has become about 30% brighter - but that is not something we'd notice on human time scales!