Oh they are holy terrors in the first few months. Then they get to be around 6 months to a year and feel like they don't need to listen to you anymore, but then they start to mature and then you end up with a really great dog. All dogs go through stages, but I found with GSD's they are extreme. My first few months with my dog were hellacious.
Patience and consistency will pay off.
Are there any dog trainers in your area? Sounds like it would be a good idea to find an experienced trainer to help get you started on the right path.
For recalls, get a training line, maybe 20' or so. Never use your recall word without being able to back it up. At my training class, we'd use the training line and our recall word, and a little pop the collar. If they were on their way back to you, the slack in the line will mean they won't feel the collar pop, but if they aren't on their way back, they will.
When they return to you, have a favourite treat or toy handy and have an absolute party, so they know coming back to you is always the right decision, even if a moment before they were doing something naughty. Never punish your dog if it comes when called, even if you caught it digging up the garden or whatever. It's always a party when they come when called.
Otherwise, just keep training sessions short and sweet. Maybe do 15 minutes in the morning and 15 minutes in the afternoon. If you can squeeze another 15 minutes in before bed, that is good too.