The way I see it there's two possibilities with a feinter line.

1. The wee you tested with was more diluted than the first lot - quite possible if you've been peeing a lot.

2. The HCG is getting less - this is less likely but still possible. I'd really only be concerned if you got a BFN in the middle of them. With my second m/c I had two positives, a negative then a positive on a digital. By the time I saw a doctor my HCG was down to 3 but I was told that to get that many positives on different brands I had to have been UTD. Two days later it was 0.