We got our BFP!

Nikki
We got a BFP! As a teenager, I took several medications for my arthritis that the doctors said I may or may not be able to carry a child. I accepted that a long time ago and said I didn't want children but if it happened I would be grateful. In February I found out I was pregnant after what I thought was my period.  I miscarried three days after a BFP and it was devastating not only to me but to my fiancé as well. He was so excited. 
​Well here we are 3 months later and I missed my period, and got a BFP! I'm super excited but he's not. He doesn't wanna tell anyone until we know it's for sure. I guess my question is, how do I know it's a for sure?