How do I know if my baby is lactose intolorant???

My baby son is 5 mths and 2 weeks old. He has ahd colic but it has gone thank god!!! What a nightmare that was!! :( I started him on the spoon when he turned 4 mths, only giving him 2 spoonfeeds of baby rice a day, one in morning and one in evening. I have since been giving him Egg custard, and some of the fruit feeds from Heinz baby food range(all from 4 mths onwards). Yesterday I bought some of the Danone Baby Yogurts. I gave him some of the banana one yesterday and yesterday evening he was really cross. Crying alot and farting alot too. Hes been ok before yesterday so I was wondering would it have been the yogurt??? I think he startin to teeth too its just so hard to know whats goin on. Do ya think its the food??? Should I cut back?? He a hungry baby. He on Aptimel Easy Digest cos of the colic. Goin to c a pediatrician before changing milk cos colic so bad. Help!!!!!!!