You may be suffering from pardem depression, common for new mothers. Contact your doctor. Talk with your fiance. Let him know your feelings for him and the reasons for your behavior and the fears you are experiencing. Let him know you need his support and that you need to contact your doctor to get some help. Don't leave him in the dark. He may think you pushed him away not understanding why. This way he has an understanding and can help you. I hope this helps. Please keep us posted. We remain here for you.
If you are having any thoughts of suicide you should get help immediatly.
I went to mental health where I live and it wasn't that bad. I was afraid someone I know would see me but they never did. It is none of thier business anyway.
It is something to try, you never know maybe it will help alot.