Lactose intolerance can be treated by taking a probiotic (acidophilus and other "friendly" bacteria that are normally present in the gut).
If you've been sick recently, have you been on antibiotics? I ask because antibiotics will kill some of the friendly bacteria in your gut and can cause overgrowth of yeast or c. difficile (bacteria), which can lead to diarrhea.
Probiotics are also needed to treat yeast overgrowth or c. difficile associated diarrhea.
Insurance may cover prescription strength VSL #3 (a strong probiotic)...or you can try to find a probiotic at a health food store. Get one that is kept in the refrigerator, they are usually more effective than non-refrigerated probiotics. And if you can swallow pills, get a probiotic that is enteric coated to protect the friendly bacteria from stomach acid, it will be more effective.
And yes, it is also possible to develop a dairy allergy at any age. But diarrhea by itself as a symptom points more to lactose intolerance or gut flora imbalance (C. Diff., Candida, etc.) than dairy allergy. But do get tested for milk allergy anyway to make sure.
Chronic Lyme, Bart., Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut dysmotility & non-specific inflammation, Lupus, Osteoporosis, etc.; G-Tube
Meds: Flagyl, Domperidone, Claritin, Singulair, Andrographis & other herbs, homeopathy, supplements, etc.