Hi,
Firstly let me congratulate you for making your baby a 3 month old bundle of joy! I wish to tell you that the weight gain of your baby is optimum as per the growth pattern of a healthy baby. The weight gain is more in the initial months and slows down after 2-4 months. Also at this age it's ok to let the baby feed when he's hungry. Urine frequency seems normal. I would love to answer more queries from you. I am available online at :
https://www.cloudninecare.com/doctors/dr-nazarath-nirmal-raj120