Brown watery discharge

Amy
On 11&12dpo I got two faint but positive hpt.  I'm now 13dpo, I haven't tested today because AF is due tomorrow so I figured I'd test again tomorrow in the hopes of getting a stronger positive.  
Anyway, as mentioned I'm 13dpo (AF is due tomorrow) and I just experienced a gush of brown watery discharge.
Does anyone know what this is?  Is it normal?
(I'm not exactly sure where to post this).