spit-up mystery

snicksnack

We have noticed over the past couple of weeks an increase in my son spiting up.  I was concerned that he may be developing a milk intolerance like DD.  DD had the mystery green diapers, spitting, and red ring.  With DS it is only spitting, not projectile just regular spit-up. He also has a face rash which I think is from constant drooling.  Well last week I went on a business trip and my mom and DH gave him a mix of fresh and frozen milk, the frozen was from July and Aug.  She noticed when he had the older milk no spitting. DH said he did not spit at all for him until after I came back and started nursing again.  Any idea what could be causing this?  I really don't want to cut dairy again if I can avoid it because it was really hard and I am thinking if it was dairy wouldn't the frozen still have effected him the same way since I had dairy in my diet then.  My diet has not changed other than going back to work and eating out more often but not a lot more often. 

TIA