Active Cat, Eating less, weight lose,very low out put of Stools like toothpaste color Brown

Cat health My cat has lost some weight but is very active and is not eating as much as she normally would, She has small amounts of stool looking like toothpaste brown in color, she had be in heat on and off for the past 2 month. She is acting like her old self, but is having this potty problem. We are worried that this could be something bad.
If this is, a hairball is there anything we can give her here at home to help pass it.
Like Butter, any oils or Glycerin..

Sincerely Yours
Rev, Daniel-Peter