PLEASE HELP!! 😱😱

Erika
LMP WAS 2/22. Been having cramps and seems to be pelvic stretching or tugging . Been getting BFN. S/O says he feels like he's been eating more and craving things he's haven't eaten in years and getting sick.    Why haven't I got a BFP YET??? When could I have conceived to where it will show a positive test . Or when should my period have started?? 
Past CYCLES 
DEC. 14
Jan 16
Feb 22
march NONE!!