Aww you poor thing. :hugs: I am the same and you are definately not a loony. I think it is only natural for us mums to worry about everything from the moment our gorgeous babies are conceived and especially when you have had a loss before. I had a scan at 7w5d and heard that beautiful heartbeat, and have my 12 weeks scan this Wednesday and have exactly the same fears you do.
I agree with lj, if you are finding that you are extremely anxious all the time, go to see you GP and explain your fears ( they get it all the time) and see if they will do some more BT or a scan to ease your mind.
Good luck!