I'm really confused!

I had a BFN 3 days ago.  I took another one just now because I thought the line would be darker.  You can barely see the line, it's lighter than the first test was!  
Has this ever happened to any of you?  Did everything turn out ok?  We had a MC last year so this really has me worried.  I go to the dr today so hopefully I will find out what my HcG is!