Is there anyone who can shed some light on this situation? Or who have been in a similar situation?

I had my last period June 15th—19th. It was a regular heavy/medium bleed period. Yesterday, June 30th I went to the hospital for pelvic pain and lower back pain and they found cysts on my left ovary. I do have PCOS so it’s to be expected for me. But what’s weird is after I came back to my room from getting an ultrasound done, the nurses told me that my urine pregnancy tests came back positive. So they also ran a blood test which came back with Hcg levels of 41. They said they didn’t see any evidence of a pregnancy on my ultrasound which could possibly mean that I’m very early, like I just recently got pregnant. But I just don’t understand how that’s possible? I have to go back in two days for a repeat test to see if my levels increase but they’re also saying this could be ectopic, but there was also no evidence of this on the ultrasound. Is it possible I got pregnant immediately after my period ended? What is going on? I just had my second child via c section 1 year ago and I also have a 3 year old.