A really bad smell coming from anus based on what I ate?

This problem has occured since the ending of March (2014), and as time goes on, it becomes worse somewhat (Symptoms change).

I'm a freshmen in high school right now, and I'm stressing over this on schooldays. My classmates also pinpointed the fact that it's coming from me, and in every class, people talk about this horrendous smell. 

Recently, this smell is based off of what I eat. If i eat meat, a few minutes later there would be this ROTTEN meat smell surrounding me. If i eat cheese, a few minutes (ranging from 5-hours) later, there will be a ROTTEN cheese smell. Whatever I ate will end up having a rotten smell. The issue is, I don't know if passes through my rectum or not, because I can't feel ANYTHING. It happens unexpectedly and it is a HORRIBLE stench apparently. My brother, who has the WORSE stenches (seriously bad), literally couldn't breathe in that air with the rotten food smell. That was how bad it was. Sometimes I smell it, but most of the time I can't. 

In the beginning (march), it wasn't related to any food stenches, but just excessive gas I guess. At that time my diet and health was horrible. I would drink soda everyday, and had no breakfast, nor lunch, and minimum amount of dinner. The breakfast i ate was cereal oatmeal, and I slept late. This pattern stayed the same for 3 weeks, enough to change my health.

Someone, PLEASE, tell me what you think this can POSSIBLY be. 

I don't care what the response is, please someone just tell me SOMETHING.

If it helps, I'm a 14 year old girl, who had severe constipation a few years back (maybe 6 years back?), and other digestive issues (that weren't really severe). I had yeast infection as well but that's cured.