ideas?

Sat here crying. I'm 16 days late for my period and every test I've taken has come back negative, they're always on time and I'm not stressed or on any medication. today I've had light pink spotting so i put a pad on and 2 hours later checked again, nothing on the pad but when I wiped there was a small amount of light pink blood, checked again afterwards and still nothing on the pad but light brown blood on the tissue and a bit more and now it's back to being light pink on the tissue and a few light pink marks on the pad. I don't what any of this means? could I of been pregnant and now not? could I be pregnant and just have implantation bleeding? was I ever pregnant? my heads in the shed :(