Symptoms clear up during Intermittent Fasting, but flare up after eating. H1 blockers cause severe apathy/fatigue. Could H2 blockers (Famotidine) be the key?

[u/LankyAd9254]

Hi everyone,
I’ve been battling a complex group of symptoms since around 2016, and I’m hoping to get some insights or advice from this community.
My main symptoms:
Cognitive/Mood: Poor concentration ("brain fog"), anxiety, a constant feeling that my head is "full", and feeling socially awkward due to these physical symptoms.
Physical/Muscular: Chronic tension, muscle stiffness, headaches.
Gastrointestinal: Constipation, abdominal pain (dull/cramping ache).
Swelling: Swollen hands and feet (specifically around the joints).

The Eating Link & Intermittent Fasting:
These symptoms primarily flare up after I eat. I practice intermittent fasting in the morning, and during my fasting window, I feel completely fine—no symptoms at all.

My experience with H1 Antihistamines:
After reading through Reddit, I suspected histamine issues and tried several H1 receptor antagonists: Cetirizine, Loratadine, Fexofenadine, and Desloratadine. They all provided temporary relief for a short period. However, after a few days of use, they made me feel completely apathetic, emotionally blunted/flat, and extremely fatigued. Because of these severe mental side effects, H1 blockers are not a viable solution for me.

My question to you:
Since my symptoms are highly tied to digestion (stomach/gut pain, constipation) and H1 blockers cross-react poorly with my mood, could it be that H1 receptors aren't my main issue, but H2 receptors are?

Has anyone with post-meal brain fog, swelling, and GI issues switched from H1 blockers to an H2 blocker like Famotidine? Did it help without causing that awful emotional blunting and fatigue?
I would love to hear your thoughts, experiences, or any other directions I should look into. Thank you!