Why Do I Smell Like Fart All The Time ?

For about the past 6-8 months now I ve had this smell folowing me around. I can notice it when I m sitting or laying down, but its fairly faint, and I know for sure it exists because of comments at school and people s body language when they re around me. It smells exactly like I just farted, even when I m certain I didn t. I m also quite sure this isn t a case of bad hygeine either, for I shower once, sometimes twice a day using shampoo , bar soap, and body wash. I wear deodorant and a light men s fragrance and always wipe my butt thoroughly when finished with my business. I take a multi-vitamin and a probiotic ( Acidophilus ) every morning with breakfast. The doctor I went to see had no explanation for my problem, and just sort of gave me an odd look when I explained my issue. If anyone has an idea or suggestion about what this could be it would be greatly appreciated, its basically ruining my life, thank you.