Allah (SWT) never gives pain to any one to make him suicidal, but He grants continuous bounties and orders Justice and fairness. Remembering Allah (SWT) is the origin and the source of peace of mind. People suffer when they go away from the justice, fairness and neglect remembering Allah. Sufferings of people is the result of their own bad deeds.
Suicide is a major sin because it come as a result losing hope in Allah's mercy as well as sinful killing. Mercy of Allah is greater than any problem, and no problems whatsoever gig or complicated can be bigger than Mercy of Allah.