Did you guys have sex after she had her period??
If you guys didn't have sex after her period than she's probably not pregnant. If you did well....
If the blood is brown it could be implantation bleeding. It happens a little bit after conception and if so there's a possibility that she could be pregnant.
If it was bright red blood it could be from something else. She should go to the doc if she's really worried (it seems she's having other problems). If not, just wait and see if she misses her period. If so, wait a few days and if she hasn't had it yet, take a pregnancy test.