Why might I feel sick in the belly constant headaches and not feeling 100% the day after unprotected sex and it is now the 4th day after and same?

Doctor can evaluate. It is possible to start feeling symptoms of a sexually transmitted disease soon after you are exposed. You might consider making a doctor's appointment to get tested for an infection. You can also discuss with your doctor forms of contraception to protect from disease in the future. In addition, if your period comes late this month, you could take a home pregnancy test to see if you are pregnant.