yes you should gain a little weight
It depends on your height and bmi. If you are healthy for your height and age then no. If you are underweight for your height and age then yes. But not too much. Don't be unhealthy the other ways be comfortable and healthy dear.
As long as you are healthy, you are A okay.
how high you are?
If you are 5 feet 0 inches then 94lb
depends on how tall you are but you might need to