Copper IUD (Side effects or pregnancy?)

(A little bit of TMI)

Hello, I recently got the copper IUD in July (July 17th to be exact). I had my baby in May and had my first period around June 21st. June-August, I’ve had a consecutive period starting on the 21st or 22nd. In September, I missed my period. It was supposed to start on the 22nd but didn’t.

However, I’ve been having spotting every time I wipe, but not enough to wear a pad (just a panty liner). It’s been like that for 20 days. I took a pregnancy test 4 days after I missed my period to which it said negative.

I was told by my doctor that the copper IUD doesn’t take your period away, only makes it a bit heavier and cramps worse because it’s non-hormonal. It doesn’t stop ovulation. I’m seriously confused on what I should do and I’m worried.

Has anyone else had this experience or something similar to it? I don’t know if it could be pregnancy or not because I know how I felt when I got pregnant last year in September.