Ur signs and symptom give an indication that u might be having either infection in ur lower abd now that can be either Urinary tract infection or Pelvic inflammatory disease ( PID) . Do u get burning micturation or any discharge from vagina.
It could also be kidney stones , ureteric colic .
U should drink lots of water and consult ur physician as soon as possible and don't neglect the symptoms.
take care ,
Have your periods been normal since having your son? Have you been having unprotected sex? If you have, even if you haven't missed a period, take a pregnancy test or better yet...call your doctor. It could be quite serious or it could be "nothing to worry about". Better to be safe than sorry.