Im Not Due For My Period, Yet About A Week

Im not due for my period, yet about a week ago I started heavily bleeding ( first day of the cycle kinda stuff- all week) no cramps like are usually accompanied by my period.. And a week ago I stopped taking my small dosage of antibiotics for kidney infection. Also been spending lots of time in a hot tub lately.... Am I having a miscarriage? Is this some sort of STI I should worry about? When I went in for my kidneys they did a pregnancy test that came back negative.