Can my son be allergic?

Don’t bash me I’m a first time mom. When I first had my baby I would give him enfamil and breast Milk but along the way he ended up being constipated so doctor gave him Gentlease Enfamil when he was around 1 month and half, he turned three months he started getting this rash kind of marks n all over his body so the doctor said he may be allergic to that kind so now I’m giving him Similac alimentum his doctor said continue using the cream that was prescribed to him n for me to give him milk plain cause I would add the cereal twice or three times a week but othe times I would put baby food. When he turned two months and half one doctor told me I can start giving it but when I told a different doctor she stated that they wasn’t supposed to tell me to give him baby food cause he still young so she said stop putting it n just give him the similac, continue using the prescribed cream, and the Aveeno to see if it’s a change. I promise in the week if giving him the similac the cream n aveeno his eczema is starting to clear up like his skin not dry itchy n etc.

So does this mean his allergic to milk or to dairy cause I started giving him breast milk n formula after birth, he is just now getting eczema around 2months 1/2 -3months but once I change from enfamil gentlease to similac alimentum is a huge difference so is he allergic to dairy?