I am a generally healthy nineteen year old female with no history or health problems or allergies.  About fifteen months ago, I travelled to Sierra Leone in northwest Africa where I spent about seventeen days.  I faithfully took my malaria pills and was extremely careful about my drinking water and what I ate.  Several months after my return, I began having problems with dairy products (yogurt, milk, ice cream, etc) when I consumed more than maybe a third or half a cup within a twenty four hour period.  I suffer from stomach pains and some times diarrhea (neither of which is ever debilitating) after the consumption of such an amount of diary products.  Several relatives are lactose intolerant and my father has a diary allergy.  Should I be concerned about a correlation between my travel and this development (I had no problems like this before)?  Or is it more likely that this is simply me developing a lactose intolerance or diary allergy and that the timing was simply coincidential?

Summarized question: Is lactose intolerance or dairy allergy hereditary or due to travel?