Why does the questioner live a sad life, though her heart is full of love for people and her intentions are pure, despite her diligence and efforts in life, and why is she not content with her children's circumstances?

This worldly life is a realm of trial and test. A Muslim must know that tribulation, in both good and evil, is a constant of life. The true believer is one who knows that this world is fleeting and does not grieve over what he has missed from it, for it is not his true home or permanent abode. Rather, the believer's true home is Paradise. Happiness is achieved by believing in divine decree and destiny, by thanking God for blessings, and by being patient in adversity. One must remember God's countless blessings, as they alleviate the burden of tribulation. The door of God must be knocked upon through supplication and seeking forgiveness. For whoever consistently seeks forgiveness, God will grant him relief from every worry, a way out of every difficulty, and provide for him from where he does not expect. Among the recommended supplications are: "There is no god but Allah, the All-Mighty, the Forbearing. There is no god but Allah, Lord of the Mighty Throne. There is no god but Allah, Lord of the heavens and Lord of the Noble Throne. There is no god but Allah, the Forbearing, the Generous" and "There is no god but You; exalted are You. Indeed, I was of the wrongdoers." God is the Remover of afflictions, so cling to Him and rely upon Him.