Irritable Bowel Syndrome Treatment

I am 37 years old, and I have been on numerous antibiotics in the past year. I get sick with colds, etc a lot. A friend of mine recommended I take probiotics every day to get the good bacteria back into my body. When I went to GNC last night, they told me I should take the 50 billion one. Is that too much to take every day? I don’t know much about this product, so any input would be greatly appreciated. Thank you so much.