I am currently 12 weeks pregnant with DC2 and have my first ultrasound on Wednesday, so of course I'll find out then the answer to my question, but just thought I'd ask for your experiences out of interest in the meantime 
So I got my BFP more than a week before AF was due. The positive appeared within seconds of taking the test and was very clear and dark. I did 2 more tests which were exactly the same. I'm confident re the timing of conception- I regularly track my cycles on the Flo App, had been TTC for about 4 months, and my periods were extremely regular (definitely had a period the month prior!)
With my first pregnancy, I was incredibly lucky and although I had slight nausea and food aversions in the first trimester, you wouldn't have known I was pregnant til about 20/25 weeks; I had no bump, no symptoms and pretty much lived my life as normal. Again, I have been very lucky in that I've had no morning sickness, but all my symptoms seem far more extreme this time. I've been incredibly nauseas, my food aversions are extreme, I have had tugging sensations in my stomach, I CANNOT stop eating and am starving all the time, and I feel as though I am starting to gain weight already. I somehow just 'feel' a lot more pregnant this time!
I know that every pregnancy is different, but I keep getting a niggling sensation that there are two in there!! Especially given the dark test so far in advance. Interested to hear your experiences 