Don't know what's causing this

Also I have a random swollen neck gland that doesn't hurt, but has been there for about a month

Blood in stool can be serious.  It can be something as minor as hemroids, or something as major as colon cancer.

How old are you?  What is your family medical history?

Make a doctor's appointment with a GI specialist.

You still poop hard pebbles, that is NOT GOOD.

That still is constipation. If it was responsible for all your symptoms, no one will know until this constipation is gone.

You need to get soft stool, please take laxatives, gentle osmotic laxatives.

As long as I can think, whenever I had hard stool (or even my young child), I would have fresh blood from it simply by ripping the poor lining into pieces like with a wire brush. (sometimes with pain, sometimes no pain at all)

Once you have soft stool, the little bleeing can still continue, it takes weeks if not months to heal ripped lining.

So fresh light red blood can be as simple as a physical wound due to continuous pebble hard stool pressing.

But you need to mention it to doc for sure. It can be easily seen if fresh red blood was due to physical (not ulcerative) lining rupture at 'bottom' end of intestine.

But you also need to get rid of this constipation.

Are you taking laxatives? Are you well hydrated? Are you taking probiotics daily?

And yes, please see your doc! Maybe get a plain x-ray to see where fecal impaction is sitting. If 'only' at the end bit, an enema might be the answer.

Maybe a clean out and colonoscopy will be done too?

Have you tried Fybogel or Lactulose?

Ask for a fecal calprotectin stool test to rule out IBD such as Crohns or Ulcerative colitis and get a blood test for celiac if worried about these conditions. Other causes such as these will need to be ruled out before IBS is considered.

If laxatives and a high fibre diet have not cured your constipation after three weeks, the reason for this will need investigating.  I had back pain, constipation, stomach pain, loose stools and nausea.  I was diagnosed with IBS after stool tests, an ultrasound, urine test and celiac test all came back negative.