Flagyl (metronidazole) at 11 weeks 4 days

I was prescribed metronidazole at my appointment yesterday for a bacterial infection that has to be treated. I'm supposed to take 2 pills a day 500 mg a pill for 5 days which I'll have to crush because their huge horse pills. I looked it up online and it said it isn't recommended during the first trimester but it didn't explain why. I asked my doctor and she assured me it was okay to take but after reading info online I'm a little freaked out about taking it but I have an appointment in 2 weeks to make sure it cleared up so I have to take it. Has anyone taken this medication during the first trimester? Thank you for any advice.