I had Egg Retrieval on 3/30, then two blastocysts transferred on 4/4, and my scheduled blood test was on 4/13. I didn't take an HPT until 4/12 and it was positive. It was the test that measures level of 25 or more. The next morning, I took 2 more HPTs, one that measures 25 and one that measures 50. They were both +. Then when I went in for my blood the level came back at 109 (this was on 4/13 which was 14 days post-ovulation; 9 days post transfer.) Everyone's levels are different so it's hard to say if an HPT would come up positive that early for everyone. I have read about a lot of people on this site who have had a neg. HPT, then gone on to get a positive in the bloodwork.
I am sure your clinic has reasons for doing things the way they do.
So how are you feeling? Did that abdominal pain go away? Are you having any symptoms?