Ok, going to attempt to post a serious response because it could be something, or it could be nothing. Either way you should see a doctor. Here's my little story...
About 3 years ago I decided to get a lot healthier; I've always exercised but not hard enough and my diet was really really bad. So I decided to clean up my diet and started eating healthier. Lost a little bit of weight (I was already fairly thin) and was hoping to start gaining muscle but couldn't put on any weight even though I was eating like a beast, and working out like a monster, and taking a good quality whey protein shake. Then came the smelly *** farts, like rancid **** that could kill a man (think of beer farts, but worse). I thought, whatever, lots more greens and more whole foods is probably the result. Oh boy, was I wrong, after a few months of nuclear *** my poop started to turn a pale color and I started getting fatigued, not just a little bit, but "holy ****, I'm 23, exercing, eating healthy, and my body is wanting to shutdown" kind of fatigue. I couldn't make it through my workouts anymore and just had to force myself to do it (and I LOVED working out before) - didn't have any energy to go out anymore and started to get crazy insomnia...
My mood started to change and I didn't feel like myself; getting short tempered, people started to annoy me. So at this point it got really scary.. I researched all this **** on the internet and it made me scared: Chrons disease, ulcerative colitis, cancer, etc etc.
I went to the doctor and got a few tests, he though it was a bacterial over growth in my colon and gave me anti-biotics. At this point I pretty much stopped working out and went back to my old way of eating (unhealthy). This was also the key... I started getting better so I naturally attributed it to the anti-biotics. So I let my body recover for about 3 months and I started working out and eating healthy again because now that I didn't feel like passing out every waking moment of the day and had energy, I had to get back on track.
Guess what? Of course the **** came back, but with a vengeance. I started getting **** bleeding (fun ;/), bad stomach pains, poo being all different colors (green, gray, yellow, wtf is all this rainbow ****?!), fatigue, mood swings, suicidal thought (yeah, wtf?).
Alright, so I went to the doctor again and I told the ****: "Give me every damn test you have, I don't care, I just want to feel normal again." I gave stool samples, blood samples out the wazoo, ultra sound, endoscopy, colonoscopy (lol, colon prep is fun, pissing out of your *** for 12 hours straight
), and a bunch of other things. At this point my colon started to develop colitis, thus the **** bleeding, so he prescribed me some stuff to heal that up. Doctor thought it might be gluten intolerance or even allergy. So I went on a gluten free diet, it didn't help. At this point I'm at a loss, and just pissed that neither the doctor, or I can figure anything out.
Then one magical ****ing day I was over my parents house for a gathering and my mom had some edamame (soy beans) laying out on the table - I ate a bunch then my stomach and forearms broke out in hives, then my lymph nodes around the neck and groin slightly swelled up.... and I thought to myself, HOLY ****ING ****, THIS IS IT!
I had an epiphany, so much **** that I was eating when I cleaned up my diet had soy in it: my stir fries with tofu and chicken, my whey protein shake which contained soy lecithin, granola bars (soy nuts), some natural protein bar I was eating had soy, every damn thing has soy, you wouldn't believe it, it's in almost every thing we eat.... even chewing gum, wtf? I went to an allergist and it turns out that I'm sensitive to soy, but never knew it because I didn't eat a lot of it, so it might give me an gurgling stomach or something when eating asian food, but nothing to cause alarm. BUT when I started to eat better I pretty much overloaded my body with soy and it made me even more sensitive to it - essentially it was destroying my insides, slowly but surely.
I've cut out almost all soy, it's really hard to avoid it 100% but I'm trying. Sixth months later I'm almost completely back to normal, not all the way but close. I've been able to gain muscle mass and my mood has returned to normal. Food allergies don't **** around and food sensitivity is the scariest because you don't know what it could be since you're not having a full on reaction to it.
Hopefully my story scared you a little to maybe see a doc and an allergist. Like I said, it could be nothing at all, or it could be a ton of different and scary things, and only a doctor can rule those out.