Pregnant or not??

B

Quick background: I had a mmc at 12 weeks in August and had a d&c. Since then my periods have been regular but longer than before. Before I was 26/27 days and now I’m more like 27/28.

Anyway now I’m either 12 or 13 dpo with a bfn this morning, but since then I’ve had cramps all day and now I have awful nausea and heartburn with a tiny bit of spotting. Would this be late implantation? Or just my period getting ready to start??