Question

Hey, I am 16 years old, 5’8 and I weigh 135 pounds.

Answer 1

Hey im a 16 year old who my best friend who is my same age and is 5'4 who has the same sitauation as you we had gone to the doctor who mentioned the thing on eating healther but that said "some people have better metobolisums than others or thie rbosy reacts diffrently to stress these things might be making your body proccess food and fat better which makes you not gain weight easaly" even hearing this she is on a helpfull eatting plan to get to her normal weight so it might be normal but it would be best to talk to your doctor just to mke sure their isnt nayhting else going on but seems like you just need a couple pounds since ur target weight should be 146 :)

Answer 2

It all depends. Are you stressed out? Usually stress influences your weight very significantly. Other than that, most people have higher metabolism than others which is why they won't gain weight much quicker than those with low metabolism. In most cases, it is not about exercise and what you eat because it is in your genes. Speaking medically, you can also get a checkup for worms in case. 

Otherwise, in my opinion, it may be normal because I am the same age as you, a bit shorter and only weigh 99 pounds. Not stressed out, barely exercise, and sorta eat whatever I want :D. However, you can get a quick checkup in case.... 

I hope I was able to help you with your question. :)