Pregnancy Spotting

My husband and I had sex on my fertile days and while I was ovulating plus a lot of other days before and after I ovulated. We’re trying to conceive. My period is now 4 days late and 2 days ago I had some brown spotting and light cramps which have now stopped. I heard some people get brown spotting before their periods come but this has never happened to me and my period is never late. I took a pregnancy test on the first day my period was due and yesterday but I got two big fat negatives! I thought the spotting and cramps could be from implantation but doesn’t that occur before you are supposed to expect your period? Then I heard the cramping and brown spotting could be from my uterus growing. Does anyone know if brown spotting (no red at all in it) could be a sign of pregnancy or have you ever experienced it?

Heavy period for 3 days (normal time), now only lightly spotting.
Normally have periods for 5-7 days.
No sex, but humped with bf (both of us had clothes on).

Ive heard many stories like just a few drops, to full periods thats some doctors classify is spotting.