How quickly should HCG go down after birth?

I commented this experience on another post a minute ago and it got me to wondering if this was normal. With my youngest child (4 years ago) my HCG didn’t zero out for about 4 months after I had her. I know this because I went in to get on birth control 2.5 months after she was born. They gave me the routine pregnancy test as usual and it came back as positive as the day I first took it. I knew it was impossible because I hadn’t had vaginal sex 😉 at all since giving birth lol This lady at the clinic looked at me like I was an idiot, as if I had any reason to lie about it, and tossed about 50 condoms and some spermicide in a brown paper bag and said I couldn’t be given birth control because the test was positive. I said “Okay I understand but I guarantee you I’m not pregnant.” She again looked at me like I’m stupid and said “Good luck” and rolled her eyes. I had to go back (to the same woman) every 2 weeks until it went away. Sure enough it slowly got lighter every time until about 1.5 months later, I finally went in, with a somewhat smirky attitude because honestly, fuck you lady, and it had zeroed out.

Looking back this probably should have concerned me more than it did. Has this happened to anyone?