Poo and sewage smell

So I just turned 14 and I've been having this horrible problem since the start of last year. Everyday I get comments (not usually directed towards me) comments such as "you smell like poo" or "something smells like farts over there" and only recently has a sewage smell started to make it's way into my life. The sewage smell only happens for like 5 minutes throughout the day but the poo smell is constant EVERY single day. I usually poo twice a day and I have 1.5 liters of water a day (recommended). My dairy and meat intake is high because I need the calcium and the protein for these crucial growing years. I know it's not hygiene since I wash twice a day and all over. I'm not fat, I'm actually rather skinny for my age. Smell does become much more apparent in a room or at high temperatures. I can smell it myself and it's either coming from my anus or my back (the odors are penetrating my skin) So I'd just like to ask all of you out there, what is wrong with me? What can I do to stop this nightmare? Any answers would be greatly appreciated. Also I workout 3 times a week.