Help?

I’m never one to make post like this so i’ll just leave my name anon 🙃 I’m a mom of 3 (4 years, 19m, and 5m) I usually know my body very well and natural family planning has always been for me. My first was a birth control baby, and it did nothing for me or my body.. However last week hubby and I were being careful like usual until we realized after he came in me that the confirm was MIA.. i literally freaked out and had to dig inside of myself to find it and pull it out 🥴 (12/19) It was completely empty.. so first thing the following morning i went and paid the $50 for a plan b pill. (were good on kids rn but won’t get fixed as we plan to expand our family again in a few years) Took it with no problems. I haven’t had a period in TWO Years! since i was pregnant and breastfeeding back to back with our boys.. Today i have very light spotting maybe enough to fill a panty liner. (12/26) only that one time and haven’t spotted since.. i’m so scared of this being implantation bleeding. anyone have experience with plan b? or have a plan b baby?? i’ll defiantly be testing in a few days/week