Hi Samantha,
I'm not in the position to recommend discontinuation of the Benadryl. (I'm not a Doctor) Yet, while researching your post, I found the following, also at Medhelp.
http://www.medhelp.org/posts/Neurology/Full-Body-Fasciculations-at-16-Years-Old/show/573009
Copy and past the entire line if needed, hopefully it will link just by clicking on it. It does discuss Benadryl. If the Benadryl is prescribed by a Doctor (even if you buy Over-the-counter pills), be sure to consult him/her before you would try to discontinue. Also, be aware of the possibility of having breathing problems if you discontinue (due to the Geographic Tongue and any swelling that may occur) if so, seek medical attention immediately. (I'm not saying this is likely).
Don't get too caught up in any of the more serious causes of the Fasciculations, as I too had them for months and they eventually went away. Try seeing if there are common causes for Geographic Tongue and Fasciculations, one listed that is common to both conditions is stress. Try reducing these. Despite our hectic world, we do not need to buy into the tense side of life, there are things that can be done to reduce stress, if this applies to you.
Hope this is of some help.
Jim