My period is late , i had unprotected sex july 18. but i have the birth control rod in my arm , could i be pregnant ?

Not likely: If you have the implantable birth control in your arm then you are not pregnant. The birth control "rod" causes irregular periods and may cause them to stop completely.

If protected: doubtful; however, no birth control is 100% effective. Monitor your cycles and get a pregnacy test.

Highly Unlikely: This birth control method is extremely effective.