First of all, you seem to answer yourself from the question i and ii. "who is liable for that (pain)" and "...manage to relieve my pain...". You mention you, God, and you leave out the devil. Yes our sins cause inconveniences in our lives. But apart from that, sometimes when you have done nothing wrong, the devil comes along himself. If you put the bible aside, you will never understand the spiritual warfare and how you "manage to relieve "your" pain". When you were a kid, you were so stubborn to your parents at home but you still stayed in school, not because you were so brilliant but because they continued to pay your kindergarten fees (when you haven't asked them to).
If you created something, say a robot, using all your knowledge in science to empower this robot, but in this case, the robot functions and has human qualities (in your image). You would be jealous if this robot gives credit to himself for any accomplishment, and not you, the maker. Then a jealous friend (enemy), comes up with the desire that this robot gets jammed up in the system, interrupting its functions and purpose. He puts things in the way to make the robot suffer, only to make the robot lose trust in you. And this makes your enemy happy. When things are bad, you would want the robot to have faith that his/her/its maker is there to guide and protect. So you try to prove to your jealous enemy that your robot will remain as loyal to you and continue to give you credit amidst all the inconveniences, even if it blames you for them.
First of all Christians believe in the 2 entities existing in the world; good and evil. The latter caused a stain in God's plan for a perfect world. This caused the first couple to be sent out of the Eden paradise and brought to a world now stained with sin, destruction, chaos (including natural disasters and those beyond understanding), a world where these forces have been at war right from the early days of creation up till now.
The war is not us against God, neither is it between us and the Devil, it is between the Devil and God fighting. Who are they fighting over? Mankind, in the center! They both fought and boasted over Job, whether he will continue to give credit to God and remained faithful if his conditions were harsh. God created all things, perfect and beautiful for his glorification. Satan did not. Losing the battle in heaven, the Devil, also a jealous and unfaithful one, is a god has come to reside in the world and rules over it, he is in charge. How do you expect the world to be?
Our free will does not mean our own power and might. It is our desire to allow who to take control over us, the will to go which way, the will to allow who to help us. We are of God's image but by default in sin and most attracted to worldly things, which are evil-infested. The devil's aim is to win the human race and turn all against God and sending man, His wonderful creation, to destruction. He also has power that is why he is able to bruise the heel of Jesus.
"And I will put enmity between thee and the woman, and between thy seed and her seed. It shall bruise thy head and thou shall bruise his heel."
He has the power to make us believe that our Creator is not the loving and faithful God He claims and therefore does not deserve the credit.
There is something we need to note carefully about Job's account. This is a man described as faithful to God. Can we say he was liable to all the pain he went through? Who was really responsible? But the bible says this about him.
"...In all this Job sinned not, nor charged God foolishly."
This does not mean Job, in his pain, kept quite. As emotional and human as he was, he complained bitterly to God, HE DID NOT BLASPHEME.
He cursed the day he was born in Job 3:2 downwards.
He questioned God because he did not understand what happened in the spiritual warfare between God and Satan. So God at last answered him in chapter 38:1-3 (NIV)
"Then the Lord spoke to Job out of the storm, He said: Who is this that obscures my plans with words without knowledge? Brace yourself like a man; I will question and you shall answer me."
"Will you really annul my judgement: Will you condemn Me that you may be justified?"
When you are afflicted, do not be judgy. Rather be strong and ask for strength in the Lord to shield you against the evil one and to keep you going. Be proud of yourself and celebrate the success as commended in Ecclesiastes 8:15 but I will end with this also for you.
"...for he maketh his sun to rise on the evil and on the good, and sendeth rain on the just and the on unjust."
This is Jesus telling us to be kind like God does. Like our parents who still showed love even when we were stubborn kindergarten kids. Know whom real credit is due.
Also check for answer in the post "Why did God come down so hard on Job"