I had my periods on 15th n we had intercourse on the 19th. i know it sounds ridiculous but been having nausea n vomiting cont. past 5 days. am i preg?

Possibly...: It is certainly possible for you to be pregnant, although there are many other causes of nausea and vomiting. I would start with a home pregnancy test. I would also recommend scheduling an appointment with your primary care physician to fully evaluate the nausea and vomiting. If you develop pelvic/lower abdominal pain or vaginal bleeding, you should go to the ER to be evaluated.

If in doubt, Test!: Unlikely from the scenario you describe but not impossible. Also possible that your, "Period" could be early spotting and you are actually 4 weeks more along than you think. Get a pregnancy test and end the doubt.