Stomach cramps, as in, the kind you might get when you have a stomach bug are not indicative of pregnancy, and neither is a fever. However, being warmer than is usual for you and experiencing period-like cramps is normal for early pregnancy.
It's possible that you have a late period because you're dealing with a virus which could be the cause of your fever and stomach cramps while your other symptoms could be attributed to PMS.
To be sure, you should take an at-home-pregnancy test. If the test is negative and you do have a fever you should call your doctor. If it's positive, you should call your doctor anyway.