Strech Marks?

So I am really concerned that I am gonna get stretch marks. I am 21 weeks now and have none so far, but have been lotioning like a mad man. I was using Vaseline brand Cocoa er w/ Shea er added, and recently purchased Palmer's Cocoa er. My question is has anyone used lotion like crazy and still gotten strech marks? If so, how bad and when did they start showing up? Also what kind of lotion is the best to use?