How to make this situation less clich� ?

The thing that usually makes this sort of story cliche is the extreme amount of angst that people put into it. It's fully justified angst, but angst nonetheless, and has been done in stories over and over again. You might try to write it with an interesting mood or perspective- or if you make the girl who gets pregnant a really interesting character. Knocked-up teens are usually portrayed as either sluts, or wallowing in self-pity. However, look at the movie Juno- she takes the whole thing with a dry sense of humor, which makes her moments of weakness even more profound. My advice is work really hard at the character development and even harder on finding an original, somewhat humorous style. Stay away from angst. Best of luck.