So sorry for your loss.
This site might be worth a look.
http://www.miscarriageassociation.org.uk/
Miscarriage is a bereavement and really a week is no time at all. I should not be a surprise to anyone that you are still weeping from time to time.
As to how long it will take until you start to feel 'normal' again, I'm afraid that nobody knows the answer to this....only that as time passes you will feel less sad.
Look after yourself and do what is best for you whether that is going back to work part time, full time or having another week or three at home.
I think it would , however, be only fair to tell your boss what has happened to you and how conflicted you are feeling about going back to work.
All the best.