Please read 😅

So i had two cycles since getting my period back post baby, had unprotected sex, had a very light two day period last month. This month my period is 15 days late and I've tested negative a handful of times. If I was pregnant I would be like 8 weeks or so, surely it would be a very dark line by now. Confused as I feel pregnant as I did with my previous children. I'm scheduled to get the hormonal iud on Monday, it would pick up on the test they do before they insert it right? I've read about people who tested negative till really late on in their pregnancies so I always think what if 😂😂