have a important question

hey guys so I had my period 3rd of March. my two ovulation days were the 16 and 17. we need bd like a week straight. well I took a first response test and it showed negative. my period due this Sat the 31. this morning I woke up dry heaving or of no where. question is the box days 3 to 2 days before period 99 percent accurate. so does that mean I'm most likely not pregnant then. or what????