HELP. I don’t know what to do

Shannon • Step Mommy 👧🏻 Nursing student💉 TTC #1

I’m very confused. 3 months ago I got off my birth control. I haven’t been late until this month...auntie flow is 12 days late, I took a pregnancy test 3 days ago and was negative. Today I’m having this...could this be fertilization? Can fertilization even occur on your period days and your period just not come? Someone help😩