I stopped when I was 16dpo. I have had five early losses and the hallmark of those failing pregnancies was that the tests just never progressed properly. This time, my tests were amazing from so early on. There was one day where the 13dpo test was the same as the 12dpo test and it just brought all the pain of thinking it was happening again crashing down on me. I waited a few days, tested on 16dpo, got an amazing line, and then decided to stop testing. I've stuck to it. For me, it would torture me. I am very tempted to get the 3+ on a clearnlue digital as a kind of milestone, but it was with one of those tests I found out I was miscarrying last time - it was supposed to go up to 3+ but went back down to 1-2 weeks. I have seen my baby with a fluttering heartbeat, but I'm still too scared!
If you're going to keep testing, beware of the hook effect. It can kick in as early as six weeks. When your hormones get to a certain point, they become too high for the tests to work properly and the result is a fainter line (seems such backwards logic doesn't it?). Diluting urine with water counteracts the hook effect.
Good luck at your appointment!