It is highly unlikely to get pregnant just nine days after conceiving on April 12. Brown spotting around the expected period date can have various causes unrelated to pregnancy, such as hormonal changes. However it's best to consult a your doctor for personalized evaluation and advice.

The pills you swallowed are supposed to terminate the pregnancy; however, this might not happen immediately. Sometimes you may go through cramps, bleed, or even pass out some tissues. It may take some hours or even days for all these to happen. Should it be that you are scared or maybe you are experiencing too much pain or bleeding heavily, please seek medical help as soon as possible. 

Sexual activities while menstruating normally minimize the chances of expectant mothers since probable ovulation is ruled out. Furthermore, chances are lowered by withdrawal before ejaculation. In the instance you also take emergency birth control pills such as Unwanted 72, chances are further minimized. All the same, there is still a small risk of getting pregnant. If one does not menstruate as expected or develops unusual symptoms, best to go for a pregnancy test. 

The pain can be because of harmonal change, muscle strain or injury. Get it checked early to avoid any further problems.