hello, usually around vacation time my anxiety tends to act up, and it makes me constantly worry and think about every tiny little thing or "mistake" I do. For example, am I slouched down a bit instead of standing up straight? Do I look or sound annoying? Then from the time I spend worrying and thinking about it, the less I enjoy the moment and then I become worried about the past and the things I missed and so on like a ripple effect. Second, I have trouble over "enjoying" things and moments, that includes the feeling in my stomach, the thoughts in my head, and more, all to just enjoy an experience. I would really really appreciate anyone's help or advice, I don't want to spend my entire life doing this.
Nick, sorry so long but I’ve been through this. everything you are doing is common with anxiety. I can tell you as somebody who has done this for decades, it’s very unsettling and it’s not a fun way of living.
when you go over things in your head over and over such as your past, mistakes, etc. that is called rumination which is very common with anxiety and stress.
I can tell you for sure that all of the ruminations, self-conscious judgments about myself, worry about how I was performing things, and on and on definitely robbed me of years and years of my life. It was so not worth it I can’t even begin to tell you.
I so wish I had learned this at an earlier age, but what helped me was finally a little bit at a time, learning that I needed to leave the past in the past!
Thinking about it was just a complete waste of my time because it’s gone. We have to pick up from where we are right now and move forward because moving backward gets us absolutely nowhere. Believe me, it’s just not worth it!
I was also self-conscious about little things also like how I was standing, what I look like, how I talked,. and on and on. I really did not enjoy life that way at all. It was a huge struggle.
Now, I’ve learned not to not put the focus on myself because I realized that most people really don’t care about the little things that I’m doing or not doing. . Most people are focused on themselves.
I also learned not to care so much about what other people think. . When I cared too much, I never really knew who I was, what my opinions were, I did not have a good sense of myself! That’s not a good thing.
I could go on and on about all of this but it would be so long! I will summarize What I have learned along the way :
LEAVE The past in the past
BE your own best friend and love who you are
DONT make others opinions more important than your own . you are just as important than anyone else.
KEEP very busy. That will take the focus off of yourself . also, when you do things for others you don’t focus on yourself.
REMEMBER that other people are not perfect and they make mistakes all the time! They just dust it off and keep going!
WORK ON Enjoying those simple things in the moment! I can tell you that life goes by very fast and we cannot get back one day that we wasted with worry, fear, self-doubt, etc. I lost years because of this. Take that walk in nature ON a beautiful day and notice everything! this might sound silly but seriously notice The tiniest little things we used to do in childhood like watching ants build their house and carry food in , lol
WHEN you get negative thoughts, immediately say to yourself either NO or delete or whatever you want and quickly think about something happy or do something that keeps you busy. Don’t get anxious about it because they get worse.
BE Fighter for yourself! Don’t let negativity and self-doubt control your life. You are in charge! You can do this! You may have some days better than others but at least you will be on the road to recover from this. It’s a gradual change but it can be done and it’s all up to you.
another thing you can do is get some counseling for anxiety. They see this every day and have the tools to help you! I have benefited greatly from just venting all of this to my counselor. It’s hard to do alone.
On YouTube you can find some great motivational talks about life by ex navy seals Called team never quit.
also on YouTube you can find some great meditations for anxiety, overthinking, etc. I listen daily. YouTube also has general talks for helping to control anxiety, racing thoughts.. there are hundreds of videos on YouTube for this!
One Day at a time. Don’t take life too seriously. be gentle with yourself. 
Your life is normal and will not be easy to change. Be thankful that you do not have physical problems.