See your doctor. Since it is the top of your belly, then it isn't your girlie parts! Not unless you are 8-9 months pregnant. Being sick can affect your cycles. Cycles also change over your lifetime. Mine have changed several times from 7 full days of very heavy flow to 2 days of flow and one of spotting and everything in between.
Retest again in a week. If at that point your symptoms are concerning you, make an appointment with your doctor.
Good luck