How to tell if you are pregnant early enough to act on it without having a regular cycle to tell?

The hormones made by an implanted embryo in the womb will emerge by 3-4 weeks after a sexual encounter. These will turn a urine pregnancy test positive at that point, which is ~ 1-2 weeks into gestation. Delay of menses caused by pregnancy would be an early indication but with irregular cycles, testing would be needed. They can be falsely negative early but retesting a few days later would turn +