Abdominal cramps...help!!

Hey all! My DH and I are on cycle 1 trying for baby #1! We BD'd last Friday, Sunday, Tuesday and tonight. My OPK said yesterday was my peak fertile day. But for the past couple days I have been feeling "flutterings" in my abdomen, and last night as I lie in bed I Was having noticeable lower back pain radiating into the front. I feel since I am (at most) 1 DPO it must be too early for these symptoms...anyone else experience this?