Ay, good question kasi maraming girls ang nag-aalala about this! Hindi ka mabubuntis if you're on injectable contraception like Depo, that's literally the point ng injection, to prevent pregnancy kahit may sperm inside. A few of my mum friends who use Depo swear na sobrang reliable siya precisely dahil dito, pero for your own peace of mind and to get specifics about your particular situation, best ask your OB or sa health center kasi they can explain exactly how your contraception works and cover all your other concerns din.