Had inplanon put in a month ago during my period. i'm late for this period which would be first one since having it put in. i know it can stop it but can it happen that quick or could i be pregnant?

Unlikely: Implanon can cause period irregularities the first cycle. A backup contraception is recommended for the first seven days after insertion. If you are concerned, you can take a pregnancy test, but if you didn't have unprotected sex during the first 7 days it is more likely that this is due to the hormones and not pregnancy.

Not if negative : Home pregnancy tests are very accurate. They are the same tests used in a doctors office. They can detect a pregnancy 7-10 days after conception. If you doubt the result you can repeat it in 1-2 days. If you were pregnant the hormone level would rise enough for detection. It's normal not to have a menstrual cycle this birth control method.