Is it even possible to be pregnant !?HELP

ok I posted yesterday I took 3 first response tests. All faint lines. I took another this morning from a new box thinking maybe other box was faulty. Welp, got another line. I don’t know if you can see it. It has color. Straight up and I can see it plain as day. I’m not questioning whether the line is there because I have taken a lot of these suckers trying to have a baby. But my question is fucking HOW! I just had a baby on March 9. We had sex 2 1/2 weeks postpartum. Yes yes I know early. Doctor knows. We have had sex multiple times since then. BUT he pulls out and I have the mirena! But I don’t think it’s from having my baby because I was having stomach pain on March 28, so went to doc. My HCG was down to a 5. how is this possible on mirena and pulling out. What’s going on? We do NOT want another baby!!! Please tell me this is still from the baby I just had