Can a vagina get a charlie horse?

Vaginal cramps? I guess you mean a 'cramp' in the vagina. The vagina, bladder, and rectum are all surrounded by muscle; any muscle can spasm (cramp). There is spasm during orgasm; painful spasm of bladder at the end of voiding could be from uti. Sometimes cramping can occur with bowel movement. You may be experiencing pelvic floor spasm, or 'proctalgia fugax' often without warning, ususually at night.