It's June 25th and I still haven't got my period yet. I've had nexplanon for 2 years and with sex we use condoms. I'm getting worried. Should I be?

No. One of the side effects of Nexplanon is irregularly irregular periods. In other words, periods aren't predicable. The nexplanon is an extremely reliable method of contraception with a failure rate of less than 1/2%. You are to be commended for also using the condoms. They help prevent STDs even if they aren't needed for contraception. Your risk of pregnancy is EXTREMELY small. Hope this helps.
No, but can do test. A urine pregnancy test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test.