Advice on a bulldog which i am fostering.?

i am fostering a very big bulldog. i have had him since yesterday. i know it is early days but he is very very depressed. (due to change of home i think) i have took him to the park twice today and took him for walks round the block 3 times. he is not eating, and he has a big flatulence problem. maybe because he is upset? can any one give me any ideas on how to get him out of his depression. i keep talking to him stroking him playing with him. but the poor sod looks very depressed.and does not want to know with anything i am doing for him. also any ideas on how to stop the flatulence problem?