@Prithul Mukherjee,
1. The mass of an object orbiting the Sun has nothing to do with the time it takes to orbit. A pebble with a mass of 1 gram will orbit in exactly the same amount of time that the Earth does. This is a consequence of Kepler's third law.
What matters is the distance from the Sun. Specifically it is the "semi-major axis" which for a circular orbit is the distance of the object from the center of the Sun (orbits can be non-circular meaning that the distance of the sun would change at different points in the orbit).
So an increase in Earth's mass has no effect on the time of the Earths rotation around the Sun.
2. Increasing the population doesn't increase the Earth's mass. The law of conservation of mass says that mass can not be created or destroyed.
People get all of their mass from atoms that make us up. We get the atoms from food we eat, water we drink and air we breath. Having more people means more of the atoms on Earth will be part of people (rather than part of something else), but it doesn't increase the number of atoms on the Earth and it doesn't change the mass of Earth.
The mass on Earth is the same no matter how many people there are.
3. Of course the Mass of the Earth can increase when things from space fall down to Earth, and it can decrease when when matter is sent up to space from Earth. I believe the mass of Earth is increasing on net (not that dramatically) as the Earth get's hit by matter from space.
This still won't affect the orbit no matter how much the mass of Earth increases.