So exciting for you!!!!
I think it's something to do with the HCG trigger injection you had before egg collection. If you test too soon the home pregnancy test may pick up on the HCG from that injection and give you a false result.
I waited for my OTD (18 days after my egg collection) My gut feeling was if it hadn't worked I'd start bleeding before then and by not testing I still had the possibility of being pregnant!! Also to let you know the only symptoms I had in the 2WW was cramping/period type pains which I'm pretty certain were from the progesterone pessaries.
Good luck

Love Alison
xxxx