Late period, negative test :/

Hi can anyone shed any light on this.... I was due on Wednesday , so 4 days late, today will be 5th. Last weekend I was in agony on left side felt like I was going to pass out and I was close to tears (I've had my left ovary removed so pretty impossible to get the pain there but I still do every month ) so this time was do much worse it went on for 5,5 hours and I felt sick with it. All week my appetite has been increased abd I've had constipation. I have been ttc for 19 months. My periods are every 27 days on ave. but wed, thur fri and sat have come and gone with nothing. I dread wiping myself just incase. Yesterday (4 days late) I did clear blue digital last thing at night = not pregnant. The only other ones I have left are the proper cheap strip ones. I chart my ovulation and had my egg white discharge- sorry for tmi and know we had sex at right time- but to be fair we do every month. So why hasn't my period come if I'm not pregnant ?