What person or what incident caused you to think that God doesn't love you? Who mistreated you? What happened? We can't change the past, but we can choose to think straight today.
Here is what that means for your life. Regardless of your past, God loves you. Regardless of your experiences, God loves you. Regardless of your failures, God loves you. Regardless of your disappointments, God loves you. He has always loved you, and His love for you is unconditional.
If you would begin to soak in that reality, what a difference it would make. Just soak in it. Let it get inside you. Let it start to flow within you. "God is love." "He loves me." "He wants a relationship with me." Really, He does.