If a pregnancy test is negative, spotting is most likely not a sign of pregnancy; it could be functional or organic. Functional spotting is caused by a hormonal disturbance which is very possible in cases where depo-contraception has been used. Depo-contraception has a prolonged effect on the individual. One of its expected side effects is irregular vaginal bleeding (spotting). Temporary lack of ovulation after coming off the contraception is also one of its side effects. Therefore, conception could be difficult in the first 6 months after coming off depo-contraception. Other, organic reasons for spotting could be infections, tumors, etc. You can visit your gynecologist to identify the cause for the spotting.