I have a question that I am hoping someone might be able to answer :-)

I am 24, married and am trying natural family planning to prevent us from getting pregnant.

I am on a 28 day cycle. On days 1-5 I had my period, then intercourse on days 7,10,12, and 15. On days 14, 15, 16 I noticed some blood spotting along with tacky mucus. I took a pregnancy test on day 15 and it came back negative. I usually never have blood spotting in between periods. Did I take the test too early? Could I still be pregnant?

Anyone have any insight for me. Thank you!!!!! :-)