im try to track my ovulatin...but my period has been crazy lately?

On October 15, 2013 i had a 4-5 day period then again november 10, 2013 but this month December my period came on the the 5th IMA having a hard time knowing when I'm ovulating because I have no idea when me period is gonna come...with that being said my period is on and when its gone i want to try to conceive!!! Plz can any help me understand when would be the best time for me to try...