Have a look at your height/ weight against the BMI index.
If u only eat protein and fat and min carbs, you are on a permanent weight loss diet (like the Adkins diet.) or you have a a very high metabolism. You are a tad thin. Would u consider taking up weight training. Speak to a dietitian and have your G.P. do a thyroid test (TSH)You can only do the best you can for yourself. Your prolly healthier than your friends,but watch that diet.
The thing is you are eating healthy by consuming pure proteins (this does not count hot dogs and any such stuff also no processed foods) and good fats (butter, virgin coconut oil and olive oil). Sort of like the Paleolithic diet..
So your body naturally will be slim by default. If you star to eat unhealthy;
more white sugars and perhaps glutens and processed foods, you may gain weight but is it healthier for you?....
If you are feeling fine then I would say it's ok :) Maybe have a doctor run some blood work and so on just to be in the clear 100% :D
Um yeah, that is light for a girl....and 50 pounds less then what I would consider "light" for a guy. I was 6 foot 200-210 pounds in prime shape at 19. Guys that weighed 150 or less seemed very light to me (when doing martial arts/judo and sports like football). If your almost 100 pounds..I mean won't a strong wind push you over?