Heather, thanks so much. I actually bought a FRER test tonight. My husband would really rather I stop taking the tests and wait until Friday when I have my doctor take a test, but now that I have started I can't stop. It just this weekend started feeling all consuming!
It could just be too early. Since you had a 3-day transfer, you're technically only what would be the equivalent of 13 dpo.
I did a 5-day transfer back in April and had a negative test 4 days after (equivalent of 9 dpo), then a very faint line 5 days or so after that (what would have been 14 dpo).
Also, keep in mind that some pregnancy tests are a lot more sensitive than others. FRER seems to be the best one.
Good luck!!!