4 days late with regular cycle

So im on day 4 of missed period and there is no sign of it in the next 12 hrs at least. I.usually have discolored "dirty" looking underwear the day before. I have a stress test tomorrow and dont know if i should cancel. I had some ClearBlue tests from 2 yrs ago, but they said negative. My husband is buying me another newer box to test with. I started the weightloss shots. But the website said the shot wont change my period...but lossing weight may change my cycle. But i havent lost much weight. Maybe 2 to 4 lbs in 6 weeks..?.. im so nervous. Dont know what to do.