Can a urinary tract infection affect your period by making it lighter and brownish?

Not likely: A simple UTI (urgency, frequency, burning, bladder pressure/discomfort) would not likely affect one's menstrual period. A febrile or kidney infection is a more serious infection affecting the body as a whole and potentially would be more likely to affect one's period. Many more likley possibilities and explanations for variation in one's period than a uti.