Thanks for posting on HCM,
Ones the sperms are released, they have a reproduction capacity of 48hours when in the vagina (i suppose it will take much lesser time when found outside in open air). We can never be so sure in your case whether your girlfriend had some sperms got into her vagina immediately after you discharged; but if she did got some into her vagina and she was ovulating, then the chances are high that she might be pregnant. Implantation
bleeding, also called implantation spotting, does not look like a regular menstrual period and usually scanty with pink or brownish discharge.
Implantation bleeding and spotting happens within 1-2 days after arrival of the blastocyst
(product formed after interaction of female ova and male sperm) in the uterus
, usually around 9 days after ovulation, with a range of 6-12 days. At that time, the blastocyst is barely visible to the naked eye, probably smaller than the dot above the letter "i". Once implantation happens the blastocyst becomes the "embryo". Implantation bleeding usually presents about a week before your menstrual cycle is due to begin (or a week after ovulation). Remember that it must not occur at all.
Well what you can do now if you are too worried is go to a hospital where a beta HCG
dosage and pelvic US could be done to determine pregnancy
(also if not pregnancy, then other cause could be identified). Consultation with a gynobs is recommended.
Hope this helps