I did progesterone suppositories and cream with my last pregnancy but didn't start until after the positive test. The reproductive endocrinologist I just saw said it's too late to start progesterone after a positive test and recommended starting 3-4 DPO. I read a warning that the topical progesterone cream can get stuck in fat cells and put off AF if you're not pregnant, which would be bad. The article advised applying the cream to non-fatty tissue, where it can be readily absorbed.
I'm interested to discover how the progesterone works for you. I'm planning to try it after ovulation from now on and hoping it helps with implantation. Good luck!