My 1 Year Old Boy Has Had Diarrhea For More

My 1 year old boy has had diarrhea for more than two weeks. Some days it looks like its getting better and other days it worsens. and he has a lot of congestion, and his asthma worsens the coughing and it makes him throw up. What can I do to help him get better. i bought him bananas and Ritz cookies.