Celiac? Crohns? Cancer?

You need to see a doctor first and let them help you figure out what it might be. Don't worry or jump to conclusions until you have an actual diagnosis. Good luck

I would address constipation asap.

But I don't know how much access you have to get e.g. some magnesium citrate (we take one level teaspoon, bubble up with some spoon full of hot boiling water and fill up with OJ as the taste is not too great and only OJ mananges it to cover making it drinkable).

Magnesium citrate and probiotics helped my daughter (similar age) much better than osmotic laxatives

(we used Movicol for half a year, this one in contrary to lactose, does not draw water out into guts, but just stays liquid throughout the guts without being absorbed).

If you can get to the pharmacy and get magnesium or something like Movicol and probiotic powders or capsules, that would be a great start.

We also eat and drink some 'praised' high in count of life probiotic yoghurts. Some are in very small plastic containers as a single dose, very sweet, so easy to mix some probiotic powders into it (again to hide the taste).

Some swear by fiber, but be careful, if you take too much at once AND not drinking enough, it can constipate more. So more is not better, stay within recommondations (e.g. metamucil). Especially when it comes to eating a 'healthy' diet, much is individual. What is good for one, might hurt another. So I for example love avocado and does me good, it has more insoluble fiber than soluble, hence is not as water dependent, but insoluble fiber can be harsh to sensitive guts like a wire brush cleaning and pushing. Oats for example have more soluble fiber, is a nice bulk, but can actually slow bowel movement down again.

It's a bit of trial and error and slowly does it, not too much of well meant 'anti constipation' food at once.

Staying hydrated (drinking water) is surely a good thing and I don't mean forcing e.g. additional 4L per day down (in contrary, at a point too much water is not good for kidneys either).

If you can manage e.g. 2L of water per day, that you would normally not drink fully and easily, that would be great. Best to put a 2L covered jug there on table at the morning knowing it needed to be gone by evening. Better well before evening since you don't want to go for pee all night long. (Depends also, how the outside/inside temperature is = sweating and how physically active you are. 2L was just a 'sitting/walking/no-running/ no-sport' 'room temperature', suggestion.)

Constipation can hurt, constipation/pellets can cause fissures and red blood on top of poo. (don't get a fright, that is very common, were constantly battling that for a year until constipation under control since healing is another story that takes time)

Lymph nodes are great work/viral bacterial fight stations

and I had a student, who had swollen lymph nodes in the back of his neck in one spot for months and then...disappeared. Sometimes infections, the work against it, can take months.

You cannot assess if it was a lymphoma or not by a blood test anyway.

So no one will just make a biopsy after 1-2 months of a swollen lymph node if not other risk factors urged for a quicker biopsy (like age over 60).

A friend had a lovely not lymph node looking nodule on the back on his neck and was a benign fat growth only. It can stay life long, but doesn't look that great.

If you look up red spots on tongue, you will find all kinds of explanations, very benign ones too. (I constantly have some red spots, but lived with it for many decades.) Petechial bleeding would be even more dots, can be 100s of dots, my daughter has very fragile capillaries and one scratch can cause 100s of blue red spots on the skin.  Also one insect bite and spots just surround the bite location. There is no cure though. It's her 'speciality' as it was called.

Keep an eye, but not constant eye, just every few days, what your lymph nodes are doing

(you are pretty good to recognise them with 15 already! Bravo! Many at your age even don't know what and where they are). 

As said, if you were battling some viral infection, it can take time.

For bacterial somehow your temperature would go really bad. 

If you have seen your doc and not worsened, that's good.

If your symptoms persist, see him/her again. 

Do you have access to multi vitamine tablets or fizz vitamine drinks? Or certain juices that have vitamines? Support your immune system.

If symptoms worsen, don't be shy to word it. Again and again. Only the loud ones are heard. 

I think with 16 you can go to doc all by yourself even not insured by yourself? Depends where you were living and how you could get there.... hm.

All the best!

It's really bad if you feel left unheard, it seems nothing urgent though like an obstruction, so you do have time, time to heal.

All the best that you get better and improve, so that you can relax seeing a turn for the better. If not please call out!