What Causes Vaginal Bleeding Post Intake Of I Pill?

Hello doc
I had sex with my wife on 4th of Jan with the protection but due to likage might be the spurm got into the vegina within 44 hours she had taken ipil
On 5th
But by 12th of Jan she is having period wch is not in her time cycle also having bodyeche
She is afraid to be pregnant
So suggest me what should we do coz don't want a baby wright now
Why this happend
Anything risky for my wife
Nythng to be worry
Plz me doc.