Hi negative and positive thoughts are bound to come it's a natural phenomena. How you do the interpretation of these thoughts is what matters. It might be helpful if you see a psychologist. He can support you in managing your thoughts and interpretation of it.
Next Steps
See a psychologist online /offline. If possible try reading this interesting article (it may be a bit clinical but a nice one) https://www.scientificamerican.com/article/negative-emotions-key-well-being/
Health Tips
All emotions and thoughts are important and made for a purpose the art of using them is a key.