Someone please help! I'm at my wits end! My son is 6 weeks old. He was originally on Prosobee for 2 weeks. We had to stop it because he became

 constipated and very fussy, crying alot, but NOT spitting up. Tried to switch to carnation milk based, but he spit up after each bottle. Tried Alimentum (Dr's advice); it was HORRIBLE; he would pass gas all day and his stomach would rumble. Tried Nutramagen (again, Dr's advice); same thing as Alimentum, although not as horrific. He's still fussy and gassy. Dr said to try carnation soy, which is what I'm about to do. Is it really easier on their tummies,...