I am 18 and I am about 5'4 so what is a good weight for me, a girl, to be at?

A range. Normal bmi is 18.5-24.9. In your case, that will come out to 108-145 lbs.
About 120# As a rough estimate, 100 pounds for for the first 5 feet, and 5 pounds more per inch above 5 feet.