My last two periods were only for less than 24 hrs(neither on the day),and the last on July 23rd, a day later I started to get major headaches and nausea that comes and goes daily. Every so often I get mild cramping, dizziness/light headed. Its now August 4th and none of them have gotten better, but I feel as though its not a stomach flu/bug. My ovulation is due in 4 days approx. and I've never had symptoms for ovulation before now. Could it be ovulation symptoms, or possibly early pregnancy symptoms with a period still...

If you are female and you have sex, you can be pregnant. Telling us symptoms is just guesswork. Take a test, and another. If negative, you can still be pregnant, but there are other things it could be too, and that's too many too list.