Confused when af is due

​Just put details in another app, saying when last af was due and roughly when I ovulated as not sure 100% and it says 2nd feb for next period. Had big cramps yesterday and the other app says I may have ovulated a few days ago? Confused as to whether yesterday could have been implantation, ovulated or simply af getting ready. I took a first response yesterday and got bfn which wouldn't have been surprising if I'm not due af until 2nd it wouldn't show anyway. So confused right now. Anyone had similar?