Why do my muscles tire out really quickly (calves, forearms too) when working out?

Are you referring to the burn? If your muscles tire quickly, that is a good sign that you have more improving to do. Push through the burn and continue to push yourself. Your tolerance for pain will increase as will your strength and endurance.

Make sure your diet is giving you enough nutrients to supply the energy you need to exercise. Make sure you're drinking enough water!

Happy to help with more specifics!

Did you ever feel so tired of human relationships and living you just don't care anymore? How did you get back motivation or grind through the 'just don't care anymore'?

Totally felt that way. Still do sometimes. I have a personal relationship with Jesus that started about a year ago. Helped in a major way for myself being able to talk to someone who wouldn't respond with judgement or talk over me, but just listen.If that's not your cup of tea, the biggest suggestion I can make

What are the most suitable magazines for a fitness rookie? What are the most popular fitness magazines?

I don't read them and I'm in better shape than most people.  There is a strong correlation.  Men's Health is the one I see the most often in waiting rooms and the one I hear people refer to the most.  Do yourself a favor, though. 

Should I work out shoulders more often than chest for better posture?

Neither one. Those are isolation exercises. Use compound exercises used by powerlifters superior to all forms of isolation which is a method used by bodybuilder. Most successful bodybuilders they build a foundation first using powerlifting elements.My sport is not bodybuilding and I don't use any