Hi Neo,
You sound really worried, so I thought I'd let you know that I used to have breakthrough bleeding, or spotting, whilst on the pill. At first, I was worried, so contactd my GP. They tested me for chlamydia (negative), so I never really had an explaination for it. I was pregnant recently, and also had what could be described as implantation bleeding, but it was just normal spotting for me and I didnt worry too much. My best advice would be to ask your gf to see her GP just to check that everything is OK.
HTH,
C