If you use injectable contraceptive regularly and a few months ago, the chance to get pregnant is minimum having unprotected sex 3 days after applying the injection. The contraceptive contraceptive acts continuously preventing pregnancy.
If you applied the first dose contraceptive this time, the chance increases depending on what period of the menstrual cycle you are in. Being in the fertile time this chance is very great.
However it is advisable to wait for the next menstruation and, during this period, to use the condom in all sexual relations. If there is a delay in menstrual periods, a pregnancy test should be performed before continuing the next injection.
Injectable contraception prevents pregnancy more does not prevent sexually transmitted diseases. Therefore, even using this type of contraceptive, it is indicated the use of a condom (male or female) in all sexual relations.