Last night I found a pack of frer lurking in the back of a drawer so did one. Lovely line darker then the control and came up straight away. So this morning I did the 2nd one, line came up straight away but much fainter! About half as dark as the control. I thought it might just be a dodgy test so went and got a asda cheapy. Again test was faint and I've just done one again now incase my hcg is higher on a sight and it looks a smidge lighter. 
Has anyone else had this happen? I'm about 8 weeks and I've been reading about the hook effect etc but I find it strange it went from really dark to faint in such a short time. The lines are visible as soon as the pee touches them but don't get much darker.
I'm driving myself nuts and I mumsnet promise I will not take anymore tests!!!!!