Puzzling symptoms: melena, constipation, bloatedness in young adult... Any idea?

Good evening!

I am a bit puzzled about my (rather vague) symptoms...

I am a 22 year-old man, currently working abroad.
Over the last 2 years, from times to times, I have been experiencing episodes of constipation, dark stools, general fatigue, bloatedness, particularly noisy bowels and much more rarely, nausea and pain. (Which may not be relevant over a span of 2 years...).
- Constipation: Lasting for a week or so, going about once every 3 days instead of once daily, and with a consistency rather of #1 on Bristol Scale instead of #3 the rest of the time (I have never had any chronic diarrhea). And this comes and goes every 2 to 3 weeks - so it's most of the time. But I pass winds well even during the episodes.
- Dark stools: They usually, but not always, come with the episodes of constipation, and can be either mixed, with clearly two distinct colors: light brown and black ; or entirely black - and sometimes, they just follow "normal" stools. (No bright red blood, no blood on the wipe, does not color the water - and I do not take any iron nor vitamin supplement).
- General fatigue: On these occasions, I just find it hard to do anything and feel like I could sleep all days: just a classical "tired all the time" complaint - but it comes and goes.
- Bloatedness: I often feel like I am full and wouldn't be able to eat anything, especially when I wake up, whether it be in the morning or after a nap. But it is not associated with any pain, just diffuse discomfort around the umbillical/epigastric region.
- Noisy bowels: Sometimes, especially during the few hours after a meal, I can feel my bowels moving and it can be noisy.
- Nausea: It happens fairly rarely, but every 2 months, I happen to have an episode of mild nausea, lasting between 1 and 5 hours - not really making me sick, just nauseous for no obvious reason. (No pain, no cramp...)
- Pain: More recently (over the past 4 weeks), I have experienced a rather severe (6/10 subjectively) stabbing pain in the right inguinal region, of sudden onset, lasting for a few seconds, coming back intermitently for a few minutes, and going away... This happened at 3 different occasions, always in the same point.
- I shall just add that I always feel a bit of discomfort should I press on my epigastric region.
- None of the symptoms have got worse in itself over that period of time.

To finish with, I don't feel like I have lost my appetite, I have not lost any weight, but whatever I eat I do not put on weight. (Still, I don't usually eat much, and avoid most fats).
I try to keep fairly active, I have never smoked and I hardly drink 5 pints a year on Xmas and New Year's Day.
None of my relatives have/had bowel or gastric disease, polyposis or cancer.
I take no drugs apart from antihistamines in springtime, and NSAIDs, reasonably, when I have headaches.
And I've never been diagnosed with any serious/autoimmune/bowel/gastric disease.

I reckon this is a whole lot of symptoms... and I should probably have seen my GP earlier, but...
The reason I am asking now is mainly because of the pain that has been dragging my attention back to these symptoms lately, even though it is probably not the most concerning sign!
Anyway, I just can't make everything fit together, especially melena and constipation...
And since I am currently abroad, I'd rather wait a bit more and see someone when I come back home!

Does anyone have any idea?

(I acknowledge that a message on a forum can't substitute for medical advice, so if you think of anything, go ahead, I will only consider it as a lay person's point of view - that's for the disclaimer :)

Thanks for having read this far!

G.