Baby is almost 12 weeks and not gaining weight.

Mercedes

My little one is almost 12 weeks, two weeks ago he weighed 12.12, last week 12.8, and today he weighs 12.7. We have been on Alfamino formula for 8 days and he is spitting up much less, but still not gaining weight. Any tips, anyone else's little ones have this problem. We've had tests on his belly they came back normal, blood work is normal, and he seems happy. Also, he does have rice in each bottle due to reflux, per pediatrician.