Cycle change

Lately my cycle has been changing. I just began a sexual relationship with my man(January 2016) my cycle dates are as followed. December 18-22, January 15-20, February 3-7, and it is due come on February 27. I'm thinking it may come on sooner cause I have been having really bad cramps the past few days. My peroid is usually normal. Can someone explain or help me understand the change in my cycle?