I really wish I had a life experience that was comparable, which I could offer advice. Aside from bereavements, as I say, I have nothing, so really dont feel comfortable saying anything without it feeling trite or hypocritical.
Even saying "it'll get better" seems stupid (even though, of course, it it true and one day this will be a chapter in your life which you actually find yourself forgetting about, from time to time)
All I can say is clearly 'heavy' work is pushing your body beyond its capability - for now - may I ask are there anything a little more 'indoors' you every used to enjoy doing, or even often thought youd always fancy taking up. airfix models, lead soldiers, painting, electrical engineering, even amateur robotics??
Sorry, as I regrettably dont know you well enough, you may be laughing your socks off at that list of things you hate or are self-confessed hopeless at, or maybe youre already a master at the lot and bought the t shirt. Basically my point is youre clearly a capable and handy bloke, who likes to keep busy, so anything that is keeping the hands and the grey matter busy, without overstressing your body must surely be a positive.
I'll pm you my address if you want to pop over and actually slap me in person for the riduculous attempt at help.