What Causes Fainting Spell And Nausea After A Workout?

Hi, I have been having what my mom and I call "black outs". Basically i can be sitting or doing anything and I won't know where I am or what I am doing (last anywhere from 2-15 minutes). I have even been in my own house and my mom would have to lead me around. Most of the time throwing up is associated with it. We have been trying to figure this out for a year and nobody has answers. We have, however, noticed lately that they seem to happen after I work out at the gym. Do you have any suggestions of what this may be?