How can I overcome my negative thoughts about myself?

Hello Friends,

I believe in positivity and positive thinking, but oftentimes I dwell into negative thoughts about my own self. I read books and listen to motivational speeches even then I occupied myself with self-negative thoughts. 5 years ago in 2015 I was diagnosed with rheumatoid arthritis, and I have learned to live with it. But sometimes it makes me feel negative about myself and my future that develop suicidal thoughts in me. I really wanna overcome this negative mindset about my health condition. I don't wanna trash myself with these negative thoughts. Can you guys please help me to overcome these negative thoughts?