The 19th would be the earliest I would test with a first response.

I'm on the same schedule as you and waiting to test on Sunday if AF hasn't shown. But the earliest you could test is 5 days before AF with first response, or any other test for 6-5 days before AF. But only about 50% of women get positives that early and every day you wait increases the chances it will read positive if you really are preggers. I just don't want to keep being disappointed with negatives. Good luck!!!✨