Me and my GF had unprotected sex. I practiced interrupted coitus and she was on her mini pills. Because we both are not prepared for this pregnancy we are worried that a pregnancy can happen. She is not getting any periods so what is the sooner that we can have a reliable pregnancy test keeping in mind we are both extremely worried

When was her last period ? I would have to say three weeks after her last period with first morning urine.

Yes, two weeks, or three weeks after her missed period.

Interrupted coitus is a fancy term for pulling out and it is not effective at all, since there are plenty of sperm in the early fluids.

And birth control pills are not 100 percent effective