ok is he neutered? and also german shepherds are nervous little ones by nature...i call them little ones becasue even though they are big and strong somewhere inside them is a wimpering lil puppy. They act out becasue they are scared most of the time...not because they genuinly want to hurt another animal or just plain mean but scared!
Where your other dgs the same breed?

it's not you m manic and than i get my lows where i won't leave the bed then i go around thrashing things and just straight up crazy, and i have a wonderful poodle/westie who is only 2 and just sleeps all day very low key and just wants to cuddle. all dogs are just so different i grew up around animals worked at vet hospitals and kennels most of my life, train dogs/handler/groom and show them.

i know you have little money...the first step is getting your guy to listen to you not just at home but out walking and about. he does sound when you started talking about how he started shaking after you yelled, he sounds like he has anxiety. and not just with you (your not causing anxiety, you are not being blamed here for anything) but anxiety in general, you know they do have meds for dogs for that but this does not seem like a serious enough case to warrant that (but some dogs do and they are insane)
the only thing i can do is say surf the internet for little training bits and videos, i would tell you to go seeka trainer out but money issues...he needs constant reassurance but a fim hand. he would benefit from you beig the alpha "dog" and him following....again is he neutered?