What is this ?

[Prince74]

I had my period 2 weeks ago, i am as regular as clockwork, always have been. Then Saturday had a day of light brown spotting, no cramps, no other normal signs, i was really shocked when i discovered this. No idea what it is, we aren't using any birth control. What can this be? Any help gratefully received.

If your period finished 2 weeks ago it's just feasible it could be implantation bleeding. Since that was several days ago you could reasonably do a pregnancy test, try a nice sensitive one like frer. If that's negative then you should go to the gp. Bleeding between periods should be investigated.
Best of luck. Hope you get the result you're hoping for