I have not had any adverse reactions to VSL#3 myself, but know it can happen with most any probiotic. If uncertain, start at a low dose and see how things go. If you tolerate the initial dose, then try ramping up your intake.
If you remain sensitive then perhaps an alternative probiotic would be worth a try. You may even want to try a single strain at a time. Natren, for example, makes three or four single strain probiotics - although they are equally if not more expensive than VSL#3.
Until the use of probiotics is regulated and better studied, trying to find the right strategy will likely take a good deal of experimentation.