Gass/Fussiness/Diaper Rash/Tummy Rash.. formula prob?

[L.A Mommy]

LO is 3 months, he was breast fed the first month and then switched to Enfamil formula. Everything was fine until a couple of wks ago when he started being fussy during the day and in the evenings. He also developed a tummy rash along with a diaper rash, so I switched him to Enfamil Gentle ease. That cured his fussiness but the diaper/tummy rash are still there. Im wondering if he is allergic to milk based formula and if I should switch him to Enfamil Soy formula Thanks to Desitin the diaper rash seems to be at bay.. any suggestions?

Oh and LO does not spit up even when I switched his formula and he is not constipated.