hi, as u rightly said 30th would be the most dangerous period for u to get pregnancy
, if ur cycles are regular. if we suppose that fertilization had taken place then this is the time of implantation
of zygote into uterus
, and such symptoms can occur due to that. a pregnancy test can be negative, it is not 100% sensitive. the best thing is to repeat the pregnancy test from morning's first urine sample without contamination. u should not hesitate in confirming the doubts. sonography
of pelvis is the confirmatory investigation. there is no harm in sharing ur problem with a gynaecologist nearby. she will guide u accordingly. there are medicine for safe abortion
for future, the barrier method i.e. condoms are best for u, these will protects u from sexually transmitted diseases and also AIDS.