Go to a doctor.
If you are pregnant, and you don't wish to remain that way, then the earlier you see a doctor, the better.
If you want to remain pregnant, then the earlier you start prenatal care, the better.
If you have an ectopic pregnancy, then the faster it can be removed, the more likely it is they can save your ovary.
If you have the flu and it's really bad, they will admit you briefly for observation and to get hydration.
If it is something else, then you will know, rather than wasting time speculating online.