O symptons but neg opk

Sarah • Mc in May 14 at 260lbs. Worked to drop 40lbs 6 months. So we are ready to start trying again while i keep working on getting healthy.
All weekend ive had nausea, headache, lower back cramps, and sensitive nipples but neg opks. Could i be getting ready to o or is my body playing tricks on me? Im suppose to o on wednesday.