40 yrs old. change in vaginal odor. have been tested for every std and all negative. odor smells more like ammonia. is this normal??

Two possibilities: One possible cause is a vaginal infection and the other is urine running down from outside of the vulva into the vagina. Urine can also enter the vagina from an abnormal connection between bladder/urethra and the vagina(fistula). Have a GYN MD examine the area and obtain a actual cause of the odor. First eliminate harsh soaps and douches before you see the MD.