If you had your period after you had intercourse, then you are not pregnant. Sometimes in early pregnancy one can have a small amount of bleeding and continue to be pregnant, however, if you really had a period, then you are not pregnant. There are many other reasons why you could have cramping and stomach pain, including gastrointestinal problems, infections, food poisoning, and numerous other possibilities. Most of these problems should resolve on their own in a few days with rest, but if it doesn't get better you should see your doctor to figure out what is causing the problem. I hope this was helpful, if you have any more questions, please let me know.