I would not take a peripheral stimulant like sudafed or any of the allergy medications with added decongestant. Pseudoephedrine will not increase any of the desirable effects of MDMA, but it could worsen the physical sideffects.
You should be fine taking a simple antihistamine though. I'd take one of the new generation of non-drowsy ones, cetirazine (zyrtec or generic), or loratadine (claritin or generic) - they work well and don't knock you out like the first generation ones do.