Windshield problems of the 2007 BMW 328

I was driving on the highway and a rock flew up from the road and hit my windshield. When I got home, my dad noticed a chip in the corner of my windshield. The next day, the chip formed into a crack over a foot long. I had to get my windshield replaced. It has only been two weeks with my new windshield and the other day I was hit by a rock again, creating another chip. So far, there is no crack. And I found forums that people also had this same issue.