Best advice is to keep working on flexibility. Take the time to work on some alternative workouts, hell they're popular with plenty of pro athletes - do the resistance bands, plenty of stretching, and keep up with the protein intake.

I went back to intense lifting right after I got a concussion and didn't feel too good for it. On one instance I felt like I was going to pass out, probably set myself back a bit doing it.

Take care of the basics now and you'll not have too much hassle when you get back to the gym. When you do, break yourself back in slow (do single sets for a while). Doctors always say "you'll know when you're ready", which is pretty sound advice. When you feel like you want to lift, you're obviously well on the way to feeling better. Concussions are known to sap the desire for a while.