Thanks for the query.
The efficacy of the contraceptive
methods depends on many factors like the time schedule maintained by the person, associated medical disorders, other medicines taken by the person etc.
The symptoms you are experiencing could be side effects of the depo. As progesterone
is the dominate hormone in pregnancy.
You better consult gynecologist and go for blood test
for pregnancy or one ultrasound
which will rule out the possibility of pregnancy.