How long do you have to wait to have sex after getting the contraceptive implant inserted into your arm?

THe doctor that did it didn't tell you? Also it's a good idea to still use condoms as the implant offers zero protect against STD's of any type... including HPV which is epidemic in the youth today (numbers of 28% infected and growing). No form of birth control is 100% effective and using both greatly decreases the odds of still becoming pregnant.

One to three weeks has been common waiting periods. You did not ask, doctor did not say ? I would suggest asking your doctor to be sure.