People who have gotten a c diff infection are definitely prone to relapse. For most, it will happen within the first 6 months after having gotten rid of the infection. I had a relapse mild infection about 45 days after my clean bill of health. It only took one round of vanco to get rid of it, and I've been c diff free since.
C diff is also a regular bacteria found in our digestive tract, it is only a problem when it over populates. That is why cultures are so important. I had a c-scope done at the tail end of a c diff infection, and it came back with a severe UC diagnosis. Of course my colon looked horrible, it had just gone through three months of infection, plus numerous rounds of antibiotics. Over two years later, at my latest c-scope, I was downgraded to mild to moderate colitis, with lots of pseudopolyps and scarring indicating a really bad, past inflammation.
As for c diff causing UC? I don't think it causes it, but if you have a genetic tendency towards IBD, I definitely think that an infection will trigger a flare. But there are plenty of people who have gotten c diff infections and gotten over them with no residual UC diagnosis. C diff is also one adaptable son of a gun, becoming more and more resistant to antibiotics. If you are interested in more info, I can provide a few links to some good sites about c diff.
Definitely get a culture performed. I'm paranoid now, and when my flare started, I immediately thought "C diff is back, and it is seeking revenge!". A stool culture showed it was just UC. There is definitely a different feel to the c diff then there is to a UC flare. BMs have a different smell, appearance, urgency. But the only way to truly tell is to get a culture done.
36 y.o. male
Diagnosed w/ moderate UC in May '06
Asacol, Florastor, VSL#3, Wellbutrin XL, Prozac, multi-vitamin, Allegra, Lialda, Colocort enema, Prednisone (trying to taper down)