After being sick almost my whole first semester (in the first six weeks I had 2 awful colds--both of which ended up in sinus infections, two stomach bugs, and bronchitis) I finally figured out if I could spend that much time being sick, I could probably spend that time sleeping instead :zzzzz .
That made all the difference. I also discovered that the extra sleep did more good for my grades than spending that time studying.
Try to avoid sugar...yeah, I know that's almost impossible in nursing school
Getting outside and running/walking/skiing helps. Makes you a lot less stressed--throw your notes on the treadmill if you absolutely have to.
It does get better, though, as you get used to things.