Your first question "is it normal not to have a period 3-4 months?
If you are pregnant then normal , if you are not pregnant and previously having regular bleeding then it is not normal.
2nd question unprotected sex and even after 4 days , you are sick , is that normal ?
As you mentioned that there is pain in the head and stomach is growling ?
Yes this is also normal because it is a clear sign of tension ( stress0.
Now question is this that there is amenorrhea
( no bleeding ) , so in my opinion get in ultrasound
of abdomen with both ovaries and uterus
and consult a gynecologist and find out the exact cause.
Get in home pregnancy
test also just for relaxation.
Good luck. Dr. HET