Missing your period and seeing white mucus after sex could mean that the lady is pregnant. Some women feel sick or have sore boobs when they get pregnant. A baby starts when a man’s seed joins with a woman’s egg. Take a test in case you suspect that you are pregnant 

While it's less likely to conceive right after having your period, it's still possible to become pregnant at any point in your menstrual cycle, including during the days immediately after your period. 
If you've had unprotected intercourse and missed a period, it's important to consider the possibility of pregnancy and take a pregnancy test to confirm.

There can be factors contributing to changes in vaginal pH balance and the occurrence of vaginal infections. Sexual activity, particularly with a new partner, can sometimes disrupt the natural balance of bacteria in the vagina, leading to infections like bacterial vaginosis (BV) or yeast infections. This can happen due to the introduction of new bacteria or an alteration in the vaginal environment.

Unexpected weight gain and abnormal menstrual cycles can be indicators of hidden pathogenesis, including hormone disturbance or polycystic ovary syndrome (PCOS). A full evaluation and adequate treatment should be obtained from a gynecologist.