Mucousy vomit in 10mth old?

Ds3 has been exclusively breastfed up until a few weeks ago when we started introducing a small bottle of formula here and there in preparation for daycare. Ever since then he has been vomitting mucousy milk once or twice a day at random times. Its really weird and now starting to occur more frequently.

Any ideas on what it could be? I have a GP appt tomorrow but I want to go in armed with ideas because they always pass it off as a virus :shakehead:

He is on organic formula but lactose or cows milk protein intolerance has crossed my mind as a possible cause maybe?

Ugh I feel for the little dude. Ive stopped all formula for now but Im not in a position to pump b/milk for daycare because I dont want to increase my supply when I want to wean him sometime soon.