Probiotics causing diarrhea??

[Deb 27]

I had to go on antibiotics twice since February for two UTI's, so I thought I'd take some probiotics.  I usually take VSL #3 and it's never given me any problems. They are very strong, 450 billion. I don't know if it's coincidence or not but ever since I took these, I've had some diarrhea, gas and loose stools. Has anyone else had this issue with probiotics?  I used to take these all the time but they were prescription strength and even stronger. My insurance will no longer pay for them so I had to buy OTC ones.