From what you are describing, your Crohn's remission is questionable, despite normal "looking" pathologies, however, I think this fecal transplant may have caused you these recent symptoms.
Remicade is a drug which belongs to the class of biologics, I'm sure you know this, which is an immuno-suppessant, putting you at much higher risk of getting infections.
And for immuno-suppressed patients-like yourself- the risk of getting infected by pathogens and/or parasites & candida through the fecal transplant from a "seemingly" healthy donor, is significantly higher!
Most healthy individuals may show absolutely no signs and have no problems in the presence of these in their gut, however, in cases like yours it can cause havoc, despite what tests may indicate (too many false negatives).
I don't know what the official warnings and contra-indications are for fecal transplants, but the implementation or rather lack of implementation of these , may have to do with the cost of patient screening prior the to the procedure, something not necessary at all in your case!!!
Press your doctors to test you thoroughly for any viral/bacterial/fungal/parasitic infectious agents, which may have been transferred by the fecal transplant.
This happened in their hands and they should be held accountable!
The other (lesser) possibility is that the c-dif already caused the damage prior to the fecal transplant.
Long term, I would suggest, you look into the SCD program and work with a reputable Functional Medicine or Naturopathic Doctor to get your health and life back.
I would suggest trying a supplement of L-glutamine to heal your gut. Nigella sativa supplement may also help - you should google it. I take it myself but I have Celiac.