the old school antihistamines are "dirty drugs" in that they affect a ton of receptors -- the typical "antihistamine" effects relate to their action on cholinergic receptors, but diphenhydramine specifically also exerts action at serotonin receptors which is not entirely dissimilar to Prozac.
So, if you want to try to ferret out what's helping you, you could:
#1 take a newer antihistamine which does not have serotonin effects (I believe that Zyrtec probably qualifies, though I haven't looked into its pharmacokinetics too carefully)
#2 try a drug which has the serotonin impact without the cholinergic effects (Prozac or similar)
You will be hard pressed to find a general doctor with specific knowledge or interest in this regard. A psychiatrist with a specific interest either in these classes of drugs, or sensory processing disorders (tinnitus, palinopsia, etc) would be more likely to have useful input.
It may also be that the simple act of getting restful sleep for 7-8 hours a night is what's helping you; if you struggle to do that without drugs then it may be sort of hard to pin that down, but I would imagine that if you put a dedicated 3-6 months into really getting good, useful sleep without taking anything, you may find a way to do that, at which point you'll have a better understanding of how that factors in to your T.