If you have previous regular cycle,then sex on due date is very much safe and chance of pregnancy
is almost nil. Endometriosis
may cause lower abdominal pain
prior to period.
But to clear doubt, confirm your pregnancy by blood test
for B-hcg /USG lower abdomen. Check the result and if you got negative again,then do the following things.
Other reasons of delayed period like hormonal imbalance,stress/anxiety,ovarian cyst/PCOD, thyroid problem,wt gain/extreme loss,irregular eating habits etc.
Need to investigate properly to rule out underlying pathology by other test like Thyroid profile, LH/FSH,blood estrogen & progesterone
level etc.So consult with your doctor and take suggestive measures.
Control body wt,take healthy diet,avoid stress with treat endometriosis properly.