I am in my 2nd trimester. Always have diarrhea, doctor said, I need good bacteria. Is it ok to take probiotic during pregnancy?

Your diarrhea could be due to the prenatal supplement that you are taking. I had this problem too during my first pregnancy and after I switched my prenatal vitamins brand, I didn't get diarrhea anymore. If this doesn't working, you can try to talk to your gynae about your intention on consuming probiotics.