Spacing after periods

I reinstalled my re placemend disk of IT (which I got in an incredibly speedy manner when ordering over the phone--much to my delight). However, whenever i type a lab value (temp 98.7), it places 2 spaces after the period. If i hit control-0, it places no space after each word, and I have to add it in. Is there a way to go back to having spaces between the words, but no space after the periods? thanks