Excel Newbie

Hi, I'm currently working with Excel on a database of challenging behaviour with a client of mine. I have the days of the month in my first column and the months in my first row. In the cells is the duration of behaviour in minutes. However when I try to chart the figures the chart appears to add up the mins. For example if the mins were 20 on 18th Jan and 30 on the 18th of Mar the graph shows a period of 50 occuring on the 18th. Can you tell me how I would get a yearly graph with each month individually mapped?
Thanks for any help Alex