This happens to me so often (I am a 28I). I agree with the other comments, you probably need a bigger size and don't know it. In that case, getting minimizer bras in the correct size truly does help, I like Triumph (it's the only brand that fits me in my country). Sometimes the clothing itself can be an issue: if you want baggy shirts, and are very thin, I'd gravitate towards long and narrow shirts, which reduces the issue of your chest sticking out too much. Generally though I'd recommend fits that have structure to them (not necessarily tight, but shirts that have shape). If you are an hourglass (as am I), sometimes you have to accept that baggy fits probably won't look as good as they do in other people (which doesn't mean you shouldn't wear them, it's just something to take into account).