What's up with the BFP and BFN?!

I took a First Response yesterday and it was positive. I took both a First Response and a Clearblue Digital test this morning and one said BFP(first response) and the other a BFN(clearblue)!! Why would that be? I can't get in right away to do blood testing and I leave Friday for vacation. I would just like some of that cleared up. Through experience from others, please. Like I said, I'm not able to get into the docs right away or else I'd ask her now too :p thanks ladies ?