So is your question really " How is God capable of continuing to be good when he doesn't receive the same in return?" Or is it more along the lines of "How can I believe the God is always good when there's so much bad in my life and in the world at large?"
And if the absolute worst thing in your life is being overweight, then you are a very fortunate person. You aren't dying of a deadly disease or condition (at least not acutely), you don't live in a war zone, you have enough and more than enough food to eat (which for much of history wasn't the case, that's why people needed to be able to store extra food energy when it was available, just like a hibernating animal). And it's a bad thing that you can work on improving unlike a lot of other bad things that people have little or no control over.