if you are on clomid then your seeing a dr for it I'm assuming. So you may have gotten sent for a progrestrone test on CD21. Do you know what that came back as? I know mine came back at 42, anything over 12 is a sign that you ovulated and because mine was so high they told me see you in a week, we think your pregnant. A week later they confirmed it all and said everything was looking good.
If you want to you can try a HPT, it may come back negative but then just give it a few more days and try again. Good luck with your tests.
The only way to know if you're pregnant is by taking a test. Give it a few days, sometimes stress of ttc can cause delayed periods. Good luck and ill keep my fingers crossed for u!