sales analyse

Apologies for being longwinded but my boss has asked me to analyse our
sales figures and individual profits to see if there is a pattern. I
have the info going back for years but the problem is
how...............
Lets say we divide the year into 24 parts - first half of the
month/second half of the month. We have 24 products and 24 customers.
I have the order size and the profit made. Trouble is every so often
we make a loss on a sales because either our customer has a fixed
price contract and we buy in at the market price or we have a fixed
price contract and the customer buys at the market price.
Where do I start please....

Thanks in hope

Smokeyone