Yesss ! You're supposed to gain 25-35 lbs !
How do you expect to not gain weight? You have a person growing inside of you. Yes. You are supposed to gain weight
Look up weight gain according to BMI and it will give you a good idea on the amount of weight you should gain according to your body type. I should be gaining up to 40lbs at very most according to my BMI (21%)
Depending on how much you weight you should gain a certain amount of lbs but of course is just the recommendation you can gain less or a bit more but a lot more isn't good and as long as baby is healthy then less is just fine.
If you are underweight you should gain 30-40 lbs
If you are normal weight 25-30 lbs
If you are over weight 15-25 lbs
If you are obese 10-15 lbs
Of course you're supposed to gain weight. How you think your baby will grow -__-