You wouldn't feel pregnant just five days after having sex. The egg wouldn't have even implanted in the uterus yet (or since you are bleeding slightly, it could be now and you would be experiencing implantation bleeding, but again you wouldn't be feeling symptoms yet). You might just be having pms symptoms, which are a lot like early pregnancy symptoms. If your cycle is abnormal, then wait two weeks from the time you had sex and take a pregnancy test with first morning urine. By then if you are pregnant, your body will have produced enough hormone to get a positive test. Good luck!
Watch your period closely. If it carries out like it usually does, then it's your period come early. If you have this light bleeding just today and it disappears tomorrow, then you may be pregnant. Some pregnancy tests are detecting earlier and earlier but if you find you are 5-7 days without a period, take a test.