I have gone through your query and understood the concern. In the current scenario, the spotting can mean an impending period mostly. Return of ovulation after the depo shot can take up to 6 to 8 weeks and hence conception soon after the wearing off of the dose is rare. Also, home pregnancy
test can read well only after 3 to 7 days after the missed period. To clarify, you can get the blood test
for pregnancy and also go for the transvaginal sonogram. Hope this helps.