I've already wasted my entire teens and 20s, current 28 years old, working as a software engineer (Full-Stack) at a startup for ~4 years. I've been feeling like a loser and not good enough for this career even though I am a sole developer for Mobile and Web platforms at this startup in a very small team. I've put in countless hours of work every day (70-90 hrs), being on-call almost 24/7, sometimes for straight 7 days for months despite only getting paid on a salary basis on 40 hr work weeks; being a loner helps with working long hours. My salary also hasn't increased much, and feel like I'm severely underpaid based on the # of years of experience but I struggle with evaluating my value in the market to determine my worth. I assumed working hard would pay off but that hasn't been the case at all; I truly believe I've been doing the opposite of "Work Smart, Not Hard". I've been trying to get back to learning DS and Algos so I can apply to places but I struggle with LeetCode, which is making me feel like even a bigger loser for not being able to solve problems.
I'm stuck in a rut, wanting to better my skills and earn a good amount of money but unable to concentrate, riddled with brain fog, and unsure of my future. My self-confidence and self-esteem are taking a hit. I am terrible at networking, so I don't have others to reach out to for tips and advice, hence I'm turning to HN. I apologize if this isn't the place for a post like this. How can I turn my directionless life around and find satisfaction with my career?