I doubt she has an allergy to your milk if shes three months old and never spit up. My guy is the same age, and definitely goes through phases. I haven't determined yet what causes it (possibly something I've eaten beforehand), but some days he'll spit up like crazy and I'll run out of clean burp cloths...other times (like yesterday), I won't have to change his clothes or anything all day and never needed to have a cloth on my shoulder.
As long as it's not an all-the-time thing, I wouldn't worry. Does she seem like she's in pain when it happens, or does she not even notice? She may just be getting too active (like my guy). He wants to play and move around and if it happens too soon after eating, he tend to overflow. :)
If it keeps ups up for the next day or two, I'd maybe give her doc a call. Otherwise, just protect your clothes and furniture! Good luck!
at 2:10 PM on Nov. 23, 2008