if you reread your post you will see you answered your own question....

question from your post...
"Im more wondering why I have started doing it"

Answer from your post ...
"I seem to do it more when I feel awkward or have a bad memory."

my conclusion based on your post.. you started doing it because you feel awkward or have a bad memory and now its just a habit that you continue to do when you feel awkward.

habits are things we do so many times that they turn into being done with out realizing it...

examples

thumb sucking when bored or tired will result in a person forming a habit of thumb sucking when bored or tired.

Twirling hair a few times when feeling certain things will become a habit of twirling hair during those times when feeling those same things.

the good news is habits can be broken.

I used to pick at my finger nails when I was feeling uncomfortable. I broke that habit first by recognizing I was doing it and then refocusing my attention. instead of picking my finger nails when feeling uncomfortable I would write on a piece of paper ..."I am picking my fingernails because I am feeling uncomfortable, why am I feeling uncomfortable? ok now what can I do about this..

I got myself some nail polish that I loved and painted my nails. and addressed the reason I was feeling uncomfortable.

A week of noticing when I was doing it and refocusing my attention from doing the habit I wanted to break worked I no longer pick at my finger nails when feeling uncomfortable.

maybe you can break your habit. you already recognize you do it and why so now its just a matter of refocusing your attention to stopping yourself from doing it. do something positive instead like noticing when you are feeling awkward and having bad memories. maybe do some journal writing, or put on some favorite music, or other self nurturing tools that you may have learned in therapy or from your doctors.