Welcome to HCM,
After going through your history it seems that you have Fever
of sudden onset which could be some kind of virus which virus difficult to say.
You can keep yourself well hydrated and if fever is high may take a Paracetamol
which is relatively safe.
If you suspect pregnancy
you should avoid taking any drug as far as possible.
Take some rest and good diet and usually viral attacks subside in 2-3 days.
If problem persist or any new symptom appear it is always better to see a Doctor, and if any investigation is required may be done and treated properly.
If you miss period go for test of pregnancy,if positive see a Gynecologist these two issues appear separate, so take care.