Hello dear,
The presence of
menstruation after an episode of intercourse rules out the possibility of
pregnancy.
However, it can be confirmed only by an
Ultrasound scan of Abdomen & Pelvis.
In absence of pregnancy, change in the body or delay in periods can be due to many other causes like
hormonal imbalance, anovulatory cycles, stress, any infection or pathology in the uterus, ovary, etc.
So, kindly consult a Gynecologist & get a proper clinical examination done.
Investigations like
complete blood count, Ultrasound scan of abdomen and pelvis will be helpful to rule out any pathological cause for her symptoms.
Wishing her a good health.
You can ask me any further queries using the below link: http://www.healthcaremagic.com/doctors/dr-polash-sannigrahi/64925
Take care.