hello and welcome to healthcare magic
Congratulations on your baby. The first thing I should tell you is that you should continue to breast feed your son. He will gain weight once adequately fed, most doctors recommend feeding on demand. You can either feed on one breast for 30 mins and alternate with each meal or feed on both for each meal. In both cases half and hour to forty five minutes is usually enough, don't let him fall asleep, you want him to feed till he is full. If he falls asleep , just stimulate him gently to wake him up and let him finish off. He will gain weight appropiately on breast milk. Infants normally double the birth weight
by 6 months and generally expected to gain 5 to 7 ounces a week. In the first week to 10 days they generally lose a little weight ( up to 10% is the highest acceptable amount) then they start to gain.
Both of my children were completely breast and they did just fine.
As regards to losing weight, again breast feeding will help here, it is estimated that a women who is exclusively breast feeding can burn up to an extra 500 calories a day. If you eat a healthy diet consisting of 5 portions of fruits and vegetables and increase the portion of vegetables or fruits with your meals to half the plate as the USDA suggests then it is likely with the calories you burn with breastfeeding
the weight will come off. You can check out the USDA website for the ideal plate and advise on healthy eating.
In terms of exercising it is advised that you should wait for at least 6 weeks and it should be moderate, remember when you exercise your body will use some of the food you eat for energy and not for making the baby's milk. You can take the baby for walks in the stroller.
So in summary , continue breast feeding, speak to your doctor if you have any concerns regarding your babies weight.