Why is ‘Aum’ not included in Mahamantra? Is it because its efficacy is already in the Mahamantra? Does Mahamantra represent all the three states (viz. wakefulness, dream and deep-sleep) that ‘Aum’ represent?

Whatever importance is accorded in the Vedanta to the ‘Aum’ syllable is accorded to the ‘Rama’ Nama in Bhakti Shastras.

Do we not need a formal initiation for the Maha Mantra? I hear and read that initiation from a Guru is indispensable for one to take up a Nama and chant it incessantly and thereby attain liberation, as while initiation, the Guru transfers a part of his spiritual powers to the disciple which creates a spiritual awakening in him. So without initiation, am I without any hope for liberation?

For the un-initiated, it is important to be initiated. However, you do not need to wait until you get initiated by a proper Guru. You can start chanting the Maha Mantra. In due course, the merciful Lord will definitely send a Guru at an apt time. At that time, you can take the Mantra from Him.

I chant the Mahamantra only when I am unable to bear the suffering in my life. I never feel Bhakti or love towards Krishna. Will Krishna help me?

Most certainly. You come to Krishna only even for mundane worldly matters. He is your father, mother, friend, philosopher, Guru, guide and well-wisher. He loves you so much – much more than you love yourselves.

I want to chant the Maha Mantra always. In the workplace I am not able to chant properly due to my work load. Still I think about Krishna. Please let me know a solution by which I can chant the Maha Mantra always.

Chant it during your off-office hours. In due course, the Lord will enable you to chant it in your mind and still carry on with your work. You are indeed blessed to reminisce Krishna always. The lovable Lord Krishna will fill your heart with abundance of eternal pure love (‘prema’).

Will chanting the Mahamantra give the same results as that yielded by Atma Vichara?

All roads lead to the same destination called liberation. What is ‘Atma Vichara’. Contemplating in order to realize the Self. This may be done, either through Bhakti or Jnaana. In either case, the end result is the same. In the other paths, you take some effort and then wait for God’s grace. In Bhakti, you depend only on the grace of God and nothing else. That makes Bhakti an easier way to attain the end-state.
Let me give you an illustration for better understanding.
A hungry person arrives at a house. The householder welcomes him and feeds him with cooked food, and his hunger is immediately appeased.
In the second case, when a hungry person enters a house, he is accorded a welcome and given the stove , rice, vegetables, utensils and other cooking materials required to prepare the food. This person has to prepare it all by himself and then partake of the food.
The former instance can be likened to the path of Bhakti, where God take care of you.
The latter instance can be likened to the path of Jnaana, where you are required to put in effort in order to attain the goal.
In the case of Jnana Marga, the lord shows you the path to attain the goal, while in Bhakti, He verily takes you to the destination.
By chanting the Mahamantra, you are having God Himself take you to the destination.

Is chanting Gayathri Mantra enough, instead of chanting Mahamantra? When I go to satsang, I chant the Mahamantra. But, personally when I am in my room, I chant Gayathri Mantra.

There are rules and regulations to chant the Gayathri Mantra. They require appropriate ‘Nyasa’s . It mandates purity and cleanliness in all respects. You can chant the Gayathri Mantra only while sitting or standing. You cannot chant it while moving about. Unlike Gayathri Mantra, Mahamantra can be chanted at any time and any place with absolutely no restrictions at all.
Hence, whenever you are pure and clean, and find the appropriate time and place, chant the Gayathri Mantra. At all other times, chant the Mahamantra.

I hear that the Mahamantra is from the Kali Santarana Upanishad. Hence, is it okay to chant it anywhere without any conditions, or are there rules associated with chanting these? I am asking this because I have heard that Veda mantras have strict rules.

Unlike the other Veda Mantras, the Mahamantra has absolutely no rules and restrictions.

During the Japa of Mahamantra should I concentrate my mind on my soul?

You would not know the exact location of the soul. Hence you will not be able to concentrate on the soul. Hence, during the Japa, concentrate on your mind.

I am chanting maha mantra and following a normal life. How long will it take to attain the Lord? I want to know whether these sufferings will be there in my whole life.

You are already one among the blessed few, picked by the Lord Himself. Don’t get bogged down by any troubles or sufferings on your path. It might be a test for your devotion and faith on the Almighty. Hold on to the Maha Mantra strongly and continue to chant it with the same love and devotion. A sparkling bright future awaits you if you remain steadfast in your chanting.

I chant the Mahamantra when at work. Is it fine to chant in the mind or should I chant only by opening my mouth?

What you are doing is perfectly right.