Sounds like you might have yourself one doozy of a Urinary Tract Infection/Kidney Infection.
Get yourself to the doctor ASAP. In the meantime, drink cranberry juice (with the lowest amount of sugar you can find) or take cranberry capsules (which you can find at most grocery stores or Health food stores. Drink plenty of water, too.
Many times, UTI's can be cause by not emptying your bladder before and after sex. During sexual activity, it is easy for bacteria to get pushed up the urethra (where urine comes out) and cause problems, by voiding your bladder after sex, you rinse out the bacteria.
Like i said, get yourself to the doctor ASAP, because if that infection gets into your kidneys, the pain can be quite intense...