Hello Friend, Good that you are seeking a help. Negative thoughts could be due to anxiety or depression. First analyze your self for any emotional disturbance. It's may happen due to over thinking about future or past incidents. Such negative thoughts can ruin your happiness and relationship.
You may need a guidance of counseling support to figure out what's happening in your mind and ways to overcome that.
Next Steps
Feel free to reach out to me online through Practo app chat for further evaluation and recommendation.