Does God care about our weight? Yes, I believe that He does because He cares about us and the practicalities of our lives, but His greater concern is if our perception of our weight, or any identity, desire, or distraction, replaces His view of us.
Happiness is not the goal of life. Happiness is a feeling—joy is a state of being. God wants us to have joy, which is that special place of resting in the hope and truth that God is and always will be.
Prayer is a conversation with God. Because our great High Priest Jesus has gone before us and torn down the veil separating us in our fallenness from God in His holiness, we can—upon confession of sin and profession of faith—walk right into the throne room of grace and have a private audience with the maker of the universe.