Keep in mind that I've never had the invega shot so I'm not talking from personal experience here, but from what I have read in this thread from others who have experienced this, YES your muscle strength is very likely to return. But it's more of a matter of when, not if. Know what I mean? And I dare say it will take some effort on your part as well, like, when you can, start doing some small workouts at home e.g. squats, pushups, situps, that kinda thing. There are heeeeaps of video tutorials on youtube for at-home workouts that can help get you started again. Is there a particular type of exercise you used to enjoy before invega?
Have you tried melatonin to help you sleep?? Melatonin really helps me, and I have bad insomnia from PTSD.
I hate to be the one to say this, and I apologise if this annoys you, but dude......you're only 19!! You're so young! There is still decades of time for you to firgure out what you want to do, then succeed at it. And I highly doubt your family is actually disappointed in you, it's much more likely that you're telling yourself that because you're feeling so down in general. Do you talk to your parents much about how you're feeling?