How to be content and be happy

I am 22 M, completed my bachelors and currently doing an internship from a good org,I am also expecting some offer letter from top B schools ,on the surface thinks seem good, I moved cities for this opportunity, did not have any problem adjusting because I had been in hostel during my undergrad, Have a decent physique but still somethings bother me I tend to overthink a lot , even if the situation is quite good but somehow I find a reason to be sad, one thing is dating which I have not been able to do, either I get rejected or I end up with someone who is still love with her ex ,sometimes I am too old or too young for her, and much more.Apart from that I get hurt from small things if someone is making fun of them then I take it to the heart and think about it a bit too much, I have gone too therapy for all this and other bad shit that has happened in my life but I was not able to find any answer I know that things work differently for different people at their own pace but I still feel frustrated, I have a habit of somehow going into forcefully sad state even though things might not be that bad ,how do I get out of this loop This is also reflected through my face as people have often told me why do I look so stressed even though I am not or maybe I am deep inside but Basically how to maintain that calm state in every situation while not thinking too much about things I don't have currently because I am just tired of constantly thinking about I could have done better,why I am not able to get into a relationship, why I am so angry,Why do I look stressed etc ,how do I get rid of this self harming cycle which I only start out of nowhere , how get rid of this mindset of why always me whenever something bad happens ( sorry for my Grammer and unstructured thoughts as it was very raw)