Yes. My understanding is that serotonin is made in the gut. If you have an inflamed gut, for whatever reason, it will affect it. It will affect your ability to sleep well. I used to have that problem.
It's taken me years to get to a more improved state. I've done the expensive, ship to you in a cooler probiotics. Didn't work. I've done cleanses, easier cleanses - which are the only ones I'll do at this point.
There was a time I craved raw garlic and ate it. What you'll need to do is switch your diet for awhile at least. Eventually you should be able to add back in complex carbs and I mean complex carbs, with all the fiber intact. The probiotics in your system feed on the fiber in complex carbs.
Personally, I never had any luck with some of the herbs - some might. I had great benefits with pure coconut oil. I ate lean meat or chicken or eggs with quinioa or oat groats, lots of carmelized onions. I still can't eat vegetables without protein or a complex carb like beans and a grain.
At one time all I could consume was soymilk, for about five years. And your stomach sounds like mine was. If you are drinking colas, get off of them and never drink them again. They will destroy your natural flora. Buy "purified" or "distilled" water. Chlorine kills the natural flora in your body. You should never drink tap water or even most bottle water, unless it specifically says "purified" or "distilled" which seem to be beneficial to me.
You need to eat things like full fat plain yogurt or kefir. At night drink it with some magnesium supplements. Make sure you are getting Vitamin C, B vitamins, Zinc and Selenium as well to boost your immune system.
Real apple cider vinegar, like Braggs or Spectrum, is a must. It KILLS candida. If you have to put a little in a glass of water and drink it, it's very beneficial. I often make salads to eat with lean protein and use apple cider vinegar and extra virgin olive oil as the dressing. This should start making you feel better. Middle Eastern food is a real good way to focus, aside from the white pita bread or white rice. If you eat rice, eat brown. Quinoa is better for you though. It is related to spinch and has as much magnesium as spinach, but cooks up like a grain.
Ditch the sweet-n-low and aspartame. If you have to have sweetener, use Stevia. Your liver is probably toxic and that alone will help.
You might also need digestive aids right now, something with Hydrochloric acid and all of the other digest aids. Get something that is well rounded. You may not be producing enough stomach acid to kill off pathogens in the stomach. Real apple cider vinegar helps with that.
Do NOT do a drastic liver cleanse, especially if you are getting diarrhea after eating. Lemon and water is great for cleansing the liver in a gentle way. If you want to sweeten it, add Stevia.
Cut back on fruits almost completely for now. And I'm going to warn you now, it may take up to 3 years of living this way to realign your friendly pathogens to bad bacteria. It's not enough to kill off the bad; you have to feed the good. Since you cannot do complex carbs right now, the kind that bulk (like beans and grains) you DO need to eat onions (carmelized or cooked are fine as you will find that easier on your stomach) and garlic (sauteed are fine also). What's in those 2 vegetables will help feed the good bacteria in your stomach.
And be sure to get as much sleep as you can. It's amazing how lack of sleep can set all of this off again and put you right back where you started. I know, if you are having sleep problems and you very well may be as the digestive track affects sleep, it might be hard. Best thing to do is not eat later. If you have to have something, make it Kefir or full fat yogurt. The tryptophan will also help you sleep. Take it with magnesium. And if necessary, take 5HTP, Melatonin and even Valerin that wonder labs puts out.
I hope some of this helps.