Hi anon 
Till six month only breastfeeding.. 
Babys weight is fine according to ur mentioned weight. 
Don't worry about it. 
Remember that solid food u can give after six month completion sharing link which can helpful for u click and check into it 
Things to know before starting solid to baby 
<a href="http://app.babychakra.com/feedpost/46982?ref=ra36738&c=app_share&pid=android_consumer">http://app.babychakra.com/feedpost/46982?ref=ra36738&amp;c=app_share&amp;pid=android_consumer</a>&amp;

Dear, babies shud ideally double birthweigbt by 5 or 6 months. at 3.5mobrhs, this is more than enough weight. . Be happy if baby is is active and meets all parameters of healthy baby. Starting solids isnt a way of adding weigjt. Plus cow milk is to be given at month 12 completion. It is pretty low on nutrition than generally thought.

Thanks mam...is he having appropriate weight???

Hello my baby is 3.5 months old he weighs 7.2 two weeks ago and yesterday we checked his weight it's 7.5 in two weeks he didn't gain much weight and when v carry him v feel very light weight nowdays as v used to feel earlier ..wts the reason he is fine otherwise .what mistake im doing ? Is he having sufficient feed he is on BM since birth should I start solid food or cow milk ?