I'm looking for an opinion

Hi guys, my husband and I are TTC for 7 months now. I measure bbt for last 3 months and I'm looking for your opinion on my last month's chart. Today is 12 days past ovulation. I was excited for my period to be late, so yesterday I took a pregnancy test and it was clearly negative (probably was still too early). Today I had some spotting in the morning and some cramps too. My question is: Do you think it's my period starting or could be implantation bleeding? Do you have similar experiences?