Google Adsense question

Okay so on my web site I am marketing a search engine. The page is just a logo, search engine and 3 ads; a banner and two small advertisements with google adsense. So here is my problem: I want each advertisement to be random, where as right now they are all the same but contain the same words (ie: on word in my header is “cross”, so almost all of the advertisements the advertisements are “ross book store, ross skiing, cross stitching” etc.). And there are no advertising images, its just text ads. So is there any way i can fix this?