Too many possibilities, especially for the internet.
And many doctors have a tough time listening to more than 2 or 3 symptoms. You may need to try several doctors. You do describe well.
My first suggestion would be to put family history at the top of the list, even though you are young, because you have had 3 - 4 tarry stools after cramping. Tarry usually means blood.
You need a colonoscopy FIRST. Polyps could be a suggestion too, and that procedure and the right specialist will be a good start.
All the conditions under IBD should be pursued. Crohn's can start at the mouth and go all the way to the anus, and you have canker sores.
New data about IBD is being discovered daily, such as bacterial infection more than stress and poor diet.
Food allergy tests should be done too, including gluten. Some of the most common ones are wheat and eggs.
DIET really has a lot to do with almost all conditions, and eating a probiotic, turmeric, and coconut oil is a somewhat pitiful approach. Just as a small example, good foods need to be eaten together. Coconut oil is neither a cure all nor something to take alone. Yes, it is hard to work out a diet that is good for you, but you must. I assume that you know which foods aggravate diverticulitis (small seeds, etc). Given that you sleep well and it's later in the day that pain starts, doesn't that suggest that food is a good topic to work harder on?
Lying down to relieve abdominal pain suggests something rare, but I won't get into that, because I believe that the above two approaches are the most important first. It has to do with how organs are arranged in the abdomen. There is a lot of room to move out of place. But it could just be trapped gas that is relieved when you lie down! No way to guess.
I'm ONLY adding this as another remote possibility, because I have a friend who had many of your symptoms, and doctors were so sure it was Meckel's that they operated there (it wasn't, it was something else, but at least they found it).
https://en.wikipedia.org/wiki/Meckel%27s_diverticulum
And he was in his 20s, so don't go by the part about 2 year old males.
Anyway, all this boils down to your entire intestinal tract, so research the best specialist you can find. Your regular MD won't mind.
[adding this later even though you probably know
https://en.wikipedia.org/wiki/Crohn%27s_disease ]
(PS: Because of pains of old age, I have been eating THC oil on home made cookies for relief, and researching the whole subject of cannabis, and finding more and more real scientific evidence, along with all the thousands of testimonials, of it's curative powers. Given how anxiety can affect your gut, I suggest it!)