Hello I've Been On The Deposit Injection For 2 Years

Hello I've been on the deposit injection for 2 years and never had a problem I had my last shot on the 4th of March had sex the next day then about 2 weeks later I had a punky brown bleed on and off for 2 days it was light since then I've been getting all the pregnancy symptoms and 4 days ago my nipples are very itchy I'm getting milk from my right boon I've taken a pregnancy test and had a blood test but have both come back negative . Could they be wrong or is there something wrong with me