Neither of those drugs are dissociatives, especially not pseudo-ephedrine. Antihistamines can cause delirium at high doses, but not disassociation it is definitely not enjoyable in any way shape or form, and pseudo-ephedrine is a weak stimulant with no recreational value, it can be used to increase wakefulness at low doses but at high doses its only going to cause negative side effects. Taking high doses of PE and an antihistamine together could result in one of the most unpleasant experiences I can imagine.
You could try DXM(dextromethorphan) but you need to find something that ONLY has DXM in it and no acetaminophen, antihistamine, nasal decongestant, or expectorant. A good thing to look for is store brand(such as CVS or walgreens) gel caps. But make sure you thoroughly read the package information and it only contains DXM as an active ingredient, you could seriously harm yourself otherwise.
Honestly, considering you are trying to use pseudo-ephedrine as a disassociative I think you probably not be taking any OTC medications other for than their intended purpose.