Could I be pregnant but getting a continual negative pregnancy test? FET induced

So, I had an embryo transfer on Wednesday 15th July.

I have been on estradiol 8mg a day 2 weeks before that date and progesterone pessaries 3 times a day.

I did a test on day 8 post transfer (thurs this week) and because I’m UK they just expect a home pregnancy test to confirm it which I did this morning twice (and one on Thursday) and all were BFN

However I’ve had sore breasts which started around Thursday and continues to be sore - this was a real symptom in my early first pregnancy (that ended in miscarriage) as well as frequent trips to the loo.

Is there a chance that I will be experiencing false negatives or is it just the estradiol build up causing the sore breasts? (Clinic closed until tomorrow so I can’t ask) and I stopped the medication this morning after testing.