If I got a BFP, then why is my BBT going down and why am I spotting?

Spotting can be a sign of a miscarriage. It could also be that you have irritated your cervix due to some recent ual activity. If the spotting is minimal than you probably have nothing to worry about, but you should contact your ob/gyn and have all of the appropriate tests done. As for your basal body temperature, I know they say its supposed to stay up, but every one is different, as long as your temp doesn't drop below 97 degrees, you are ok.