My Negative Thoughts Are Ruining My Life: How Can I Stop Them?

Hi I am very troubled with negative thoughts for quite sometime. Thoughts about putting someone down or any activity not going to go right or imaginary argumentative conversations leading to me showing down the other person keeps preoccupying my mind. Basically I am trying to show down the other person or situation and trying to win my hand or situation. It keeps me occupied majority of the time even when I am driving, taking a walk or running, eating, during meditation as well. For real events like if I have to go buy something, I imaging the seller cheating me, giving me faulty product or not charging me more etc., while in reality it may not happen and I will take a sigh of relief. I was not like this. I was a very happy, positive & optimistic as a child, throughout school, college, at work and used to be an inspiration to many. I think my ruminations have slowly commenced as I grew in age and slowly the positivity has lead to negativity & anger. I am in fifties now. I have been trying to practice Vipassana meditation, trying to get back to exercise but it is not helping. This has increase multifold as in my daily interactions, I always find people/friends poking fun of me and trying to put me down and I fight back even though knowing that it will be of no use. I am nice to my friends and people around me but they are not the same to me. Due to this I am beginning to reduce my interactions and get away from the abuse. Though I feel that I still look at everything in a positive light but the negative ruminations due to the everyday insults / slights have begun to bother me a lot and not able to have positive thoughts. Interaction with family is also suffering. Once upon a time I had many friends who I could talk to freely without prejudice but now I don't as most of them are not nice anymore even when I am very nice, positive & encouraging with them. I hope, I made some sense. Seeking help and guidance.