I completed my PhD in mechanical engineering in December 2019 and took a break of two months after it. My topic was finite element modeling of additive manufacturing process. I was supposed to join my PhD advisor for an interim postdoc position from February 2020, but faced some administrative issues causing delay. However, come March, with Covid, my official appointment was delayed till June.

I started doing postdoc with my PhD advisor since June last year. The contract ends the end of this year but will be renewed according to my advisor. I was productive during the first 7-8 months. I published 3 papers (PhD work), submitted 1 (postdoc work) last year. About to submit two more (Postdoc work). However, I am feeling less and less motivated as days passes.

I am doing quite different work than my PhD, so there's a lot to learn. I have collaborated with 3 different groups and different universities. But I am not able to concentrate on my work as I used to during my PhD. Also, my applications for industry jobs or other postdoc positions, which are scarcely available at the moment, are disappearing into the void. I am not getting any response.

I don't feel motivated anymore and I constantly feel lacking purpose. I should be brushing up my programming skills for job search, but I can't bring myself to do it.

I don't feel competitive and I have a constant feeling of regret and remorse about my past decisions. I shouldn't have pursued a PhD. I should have chosen different field of research. I should have taken more courses. I should have worked harder. I am dumb enough for a master's degree. I did not take my career seriously and now am facing the consequences.

I am an immigrant in the current country of residence and I have not been able to visit my home since two years. I think I am ruined and absolutely doomed. I can't see any joy in things. I am already 31 and I don't feel like meeting people, making relationships or carrying out hobbies. Who would want to be with a failure like me?

I don't know what to do now. Please advise.

Congratulations! That is a lot of work to get nearly 6 papers and is a significant achievement. Don't put yourself down by focusing on what you have failed to achieve and look at what you have achieved. I can understand how you are feeling as I am going through something similar but I try to not diminish my own achievements. If you get 6 papers that is a significant body of work for such a short time and no-one can take that away from you. You have done well and that many publications is not a fluke.

What to do going forward, considering I am still a PhD student, I am probably not the best person to be talking with. Though, I would take a couple of weeks break and do the things you want to do. The hobbies you have ignored, go do them. The friends you have lost contact with, talk with them. When I have longing to do something, the only thing that fixes it for me is doing them and afterwards I have a clear head. Trying to work yourself constantly causes burnout and sometimes listening to your subconscious fixes everything.

It's very normal to feel a postdoc is very jarring after a PhD. In a PhD, you're paying (or a funding council is paying), for you to do a PhD. You can focus 100% on your research.

In a postdoc, you generally have the first experience of what academic life is like. When you have to fit your research around teaching, admin, and painfully align it to the whims of funding councils and project descriptions of work. I've never seen a PhD scheme that adequately trains for this.

This is irrespective of field. You've actually done extremely well to publish so much in the first year of a postdoc, and get an indication your contract will be extended. In my postdoc I had to repeatedly pull in funding to avoid redundancy.

It's very hard, if you're down, to listen to the argument others have it worse, but try to consider the majority of people at age 31 also have no idea where their life is going, and do not have the CV you do by a long stretch.

I feel a bit bad I can't really tell you what to do, but can only tell you what you're experiencing is normal and will (in my own experience) get better. I would say, try to contextualise Covid, since some of the things you mentioned seem related and will, ultimately, pass. Really you don't sound like you need advice to be a better academic; you need someone kicking you up the backside post-Covid to go out and meet people, so the academic issues pale in comparison :)