11dp bfn and then a bpf?

Jackie • Baby boy born 10/17/16 Baby girl 09/14/18 🤰 with #3
Had a negative this morning,I swear there was the faintest of faint faint lines starting on it.But I'm counting it as a negative.
Any ladies have a negative at 11dpo and get a positive later?
My cycles are usually 27-28days,Today is cycle day 27.but glow says af is due the 30th which would be a 30days cycle which I've never had before.