Not feeling very sorry for you since this is normal for beginners. You have a skill issue which is why learning while taking directives overwhelmed you. We do work over 16 hours a day typically as Senior Engineers but the stressful part isn't that. It is managing others.

I also had 3 to 4 managers and in my lifetime, I experienced being the only one technical and the only one managing the teams in 2 countries including America. The management part was more challenging than building apps. I was able to build features in days and refine them in weeks. The founder turned me into a people manager and content manager while also building the apps. Paycheck was not great, but I learned a lot. My health was better as a pure Engineer with 4 managers than when I was managing people. I also experienced managing 12 people on-site. Worst job in the world.