I am about 10 pounds underweight and am short at 5'2". I eat 1200 calories a day... Very slowly losing weight. I need to maintain and gain a few pounds, about 10. But I'm worried to increase my calories, worried my metabolism is too slow now. I don't seem to gain weight any time I've had a day where I've had 1400 or even 1500 calories, but it's rare. I'm just afraid to increase due to this, so I haven't. It's not like I'm starving, but I know I could eat more.
No, it could mean your metabolism is very fast. But you probably don't eat enough. You need to eat a lot more.
No it means the opposite, but it's not like you should go crazy eating junk food to gain weight. I would eat healthy foods that will help you gain weight, like lean meats.