Likely Chlamydia. The usual std's can cause pelvic pain by rash, itching, etc., but the biggest cause of pid or pelvic inflammatory disease is chlamydia trachomatis, which is also sexually transmitted. This can cause lower abdominal, and pelvic pain, and a mucopurulent (pus-like) vaginal discharge. This is a very destructive disease which can require 14 days of antibiotics, like Doxycycline and clindamycin.
Yes, but.... .. The use of condoms reduces the risk. But condoms are not 100% effective.
Yes. Depends what you call safe sex. Acquisition can come from many routes. Kissing can transmit herpes. Condoms break, etc, etc. Know your partner!
Unlikely. But sometimes, ascending pelvic infections associated with atypical bacteria have followed iud insertions, vaginal delivery, miscarriage, and uterine instrumentation.
Nope.. Pelvic inflammatory disease is the result of infection with sexually transmitted agents. No sex = no pid.