Helena- That is SO crazy. The same thing happened to me yesterday. I got a positive on an OPK. And I'm only 4 DPO. I think it was a bad test. Cuz when I did another one a few hours later it was negative.
I'm sure I O'd on cycle day 16-17. As I was using CBFM and OPK's and both had a clear positive.
I have had NO symptoms. And our timing was completely off. So I don't think I'm preggo.
Symptoms are a promising sign
Hope you see a BFP for Valentines!!
It seems a lot of us are planning on starting test on Valentines. That was what I was thinking of doing. Eventhough I know I'm not preggo. I'm a POAS addict so I can't pass up a chance to test.. 
Hope we all see BFP's ladies!!!!