How long after sex is it normal for symptoms of pregnancy to occur?

I had sex with my gf 6 weeks ago, and she complained about having period pains almost 3 weeks ago, around the time she was due for her period, in which time we had sex again... She missed her period and now she's been complaining of nausea, headaches, pains in her abdominal area, and has bled twice but only a little, ie droplets... Is it normal to be getting symptoms of pregnancy 6 weeks later or even just after a due on period, ie 3 weeks???

As a 23 year experienced pediatrician i can tell you that your girlfriend is pregnant! symptoms can occur anywere from 5-10 days after having sexual intercourse. so yes, it is completly normal to get pregnancy symptoms 6 weeks after.