I wish I had some advice to give. Your clinical experiences vary so much depending on where you are. I had really good experiences which were very family friendly - but I am sure my clinical years were the exception vs the norm.
Try to talk to people ahead of you on each rotation to see if they have any advice on who to go to for help, particular books or issues you should be well versed on.
My favorite advice for every stressfull event in my life is to make sure that I don't worry about it ahead of time. Even if your ms3 year is the worst year of your life (and it probably won't be!), it is only 12 months - don't make it 14 months by starting to worry about it now!
Pretty generic advice - I remember that I was really stressed out about starting my ms3 year because I had not had any real previous clinical experience. I just wanted to respond to let you know it is nothing to stress out about. Good luck