help with formula!

Need some advice!? My baby boy is almost 6 weeks old and stated on formula around 3 weeks old due to low supply of breast milk. He first started in enfamil newborn but was very fussy and had a lot of gas pains so my doctor recommended enfamil gentlease and he hated that. It smelled bad and he would never drink a full bottle of it so about a week ago I switched to Similac sensitive. He seems better but still having a lot of gas and still very fussy during the day. Any recommendations??