How Early Should One Test For Pregnancy While On Duphaston?

I am 40 years old - trying to conceive - have been on Clomid 50 mg for past 2 months - both times had 4 folicals ready - ovulated just fine - Progestherone levels very high after tested on day 23 of cycle- or 10 dayse after ovulation .Dr ask me to see him on day 16 after ovulation because he thought I might be pregnant - on day 24 I had like an light implant bleeding - and then on day 26 had like a period but only for 24 hours - even less - not that heavy as always only for 24 hours - I phone my dr and he wanted to see me straight away - then on day 28 I went and see dr - he did a sonar and then saw the fetus well to him it looks like the fruit bag and then also told me to start using Duphaston one a day for 10 days and toldm me that if I do not start with heavy period after day 7 of using it then have to go to do a blood pregnancy test - i did a homepregnancy test on the 3rd day of using the progesterone medicine and it was negative - what is the changes of doing it perhaps to early - what is the reasonf for me to test if possitive only on day 7 of usage on Duphaston?He also told me to contact him immediately if I would start with my period while on the progesterone .