Can someone share about Pelvic Inflammatory disease symptoms?

I and my girlfriend are in a very serious relation and from last few weeks she is bleeding between menstrual periods and there is a Pain during sex. When I asked one of my friend he said his girlfriend has also faced a same problem and he said it is Pelvic Inflammatory disease symptoms. I don’t know is he right or not? Can some one tell me few more symptoms of Pelvic Inflammatory disease and how it occurs?