I had the same diagnosis, PID. One day, out of the blue, a nurse said I shouldn't worry about the diagnosis of PID because it was sometimes used to justify the insurance payment. (gasp!) Until then, I had no clue that PID was anything other than "pelvic inflammatory disease," or that I should be concerned about any hidden meanings or connotations.
In fact, my "PID" came about secondary to a horrible infection I got from an IUD. I've always thought that the doc (who had problems of his own, for sure) purposely contaminated the thing as he inserted it. It hurt from moment one and within a week I had a raging fever--had to go in for a D & C.
I had had an IUD years before with *no* problems. They did a good prep (betadine douche, etc.), used a mask, sterile technique. This second guy did nothing, nada. He was an MD with a big practice in OB/GYN, and I trusted him because he seemed to have a good reputation. I think I'm lucky all I got was PID, a lot of pain over the years and an eventual hysterectomy. I easily could have died.
So here was my horrible infection, one single course of antibiotics, I dunno, whaddya think? Maybe it had something to do with all the PID I had later?
So, no, PID doesn't always come from STD's. But since a lot of women who have PID also have STD's, and the STD's probably were a contributing factor in those cases, there is either a) the misconception that all PID's are r/t STD's or b) a lot of us who have inflamed pelves who are being misdiagnosed.....
We oughta start a support group. Take care of yourself, hon.