Both topical clotrimazole
and oral metronidazole
will come under category B in pregnancy
according to FDA.
Means animal studies didn't show any adverse effects on fetus whereas sufficient human studies are lacking.
So if you are afraid of side effects better use topical clotrimazole only till consulting your doctor.
By this the symptoms of the infections can be controlled to some extent.
After consulting your doctor if he recommends you can use metronidazole for 3 days which can also show the desired effect.