Don’t be too hard on yourself.
You can do all the gym work, strength conditioning etc that you want and be strong for your size but if you are physically small then you simply will not be as strong as someone who is significantly larger.
Having reached the ripe old age of 38 my body is now pretty much buggered from constantly abusing it. Final straw was last year when I burst 3 tendons in my right arm from lifting things I should have been using a loader to do but stupidity reigned instead of sensibility. They are now so damaged that at some point I’m going to need tendon grafts when they go again.
By all means, keep fit and active, especially if you enjoy it, but work smarter, not harder. Your body has to last you until you pop your clogs and you won’t be thankful when it starts to fall apart. I wake up and go to sleep every day in pain and I wish I’d not done some of the stupid things I have. Getting stronger for work is generally not such a good idea and nobody will thank you for destroying yourself, least of all you.