confused

 PLEASE HELP?? Comments and opinions needed. 
Hello I have a regular cycle lasting 31 days. On this app it says I do not go in my fertile window until 5 more days . Today marks day 9 of my cycle and my periods last 5 days so it's been 4 days off my period . I've had cramps on one side today "left side" mostly mild. Could this be early ovulation??