Pos. then neg. OPK in one day?

Ok so today I'm 11 days into my cycle. My period ended 5 days ago. Today I tested positive on my OPK at 8am. Then around 2pm it was negative. Anyone experience this? We BD yesterday and today just to make sure. Can u have a false positive on your OPK? I feel like day 11 of my cycle is a bit early to test positive OPK, but I dunno- thoughts??