I just had a baby six weeks ago and had sex with my partner and he injected his sperm an me could I be pregnant and if so how soon can I take a test to see?

Yes, you could be pregnant. Wait until a week after your missed period to test. If you have not resumed having regular periods yet, I would wait three to four weeks after the encounter and take a test then. You also can ask your doctor at your six week post-partum app.