Why Did I Miss My Period This Month After Having Unprotected Sex And Missing My 3-month Injection?

Good morning Doc, I normally get my periods every 25th or 2 days after the date but i didn t get my periods this month and I had an unprotected sex and as well I was on injection of 3 months I never went since June for my nxt date, bt in July I did get my periods as normal nd heavy as it used to be.