First time posting. Need some helpful advice

Period is late. According to the app was suppose to come on September 13th but monthly visitor has not arrived yet. I have taken some tests and they have came out negative.

I have had protective sex, and since my last period on August 17th; I have been working out more(walking on the treadmill between 30-1 hr), lost some weight from last period and watched calories intake.

Not sure what to do next? When would be another good time to test? Thank you!