Why should you not have regrets?

I am an overthinker. I think so much that I forget to live in the present. I love to think about my past and analyze, over-analyze every choice I made, every turn I took, every word I spoke, pretty much everything I did and everything I hadn't done. Needless to say, I regret all my past. If given a chance, I would love to go back and change everything. But I wonder, if I had an opportunity to change my past, would my future self be happy or still regret?  Because I make decisions based on what I feel is right at that moment, in that situation and at that phase of my life. I was a different person at that person at that moment and that person felt that was the right thing to do. I've evolved and I'm a different person now. I may have become good or bad, but I'm different. This new person may not be able to fathom the past situation and envision the rationale behind the old person's choices. Anyway, what's the point in thinking about the past when I can't change it, and even if could, miraculously, would I learn anything at all in life? Would I evolve at all? I'd be the same person all the my life. I don't want to be the person that I was a few years ago. I've lived that life and I'm not that person anymore. I have learned my lessons. I have evolved.

If I don't want to change my past, all I am left with is present and future. At least past is real, future is an imaginary world that I created where all my wishes come true, all my dreams fulfilled, where I'll live a happy and satisfactory life. I despise my past self and I love my future self. Because, I think I could be a better person yesterday and I am hopeful I will be a better person tomorrow. By the way, where has my present gone? The moment I start to think either about the past or future, my present has become past. Even before I realize, my future became present, and my present has become past. Can I ever catch my present if I think? 

Isn't it a greatest discovery of life that the only thing that exists in time is present. The present is all you have before it turns to past - the past which you can't change and the future that doesn't exist. All I have to do is to live in this present moment, with all my senses awake, and with my mind fully aware. 

There is nothing behind nor in front. The present is the projection of both.