Thought you got your period but was pregnant?

I'm 13 dpo and have had brown spotting all day. Af due tomorrow. Also some cramps so I thought for sure af is on its way. But I'm also quite nauseated (maybe cuz I'm so upset about af) and super constipated. My boobs are huge (but non tender). I think I may be just reaching out for something that's not there but had anyone had spotting so close to af and had a BFP after?