Thank you for posting
All methods of birth control are not 100% effective including implants such as zarin. So pregnancy
even though a less possible could occur. According to the manufacturers zarin is among the most effective birth control methods and so pregnancy becomes very rare but possible.
Since it is possible, I will suggest you give it again a few days to observe the symptoms and the changes in you, then you can do a pregnancy test. The symptoms you have presented are among the negative side effects of subcutaneous contraceptive
You will need to discuss with your doctor about the continuous use of zarin if pregnancy comes negative.
Hope this helps