I understand your anxiety. And it's hard that the advice is conflicting.
If it's a Category B drug, the FDA has already told you that it has been tested in animals and has either not been shown to be harmful, or that it has been tested in pregnant women and has not been shown to be harmful. This isn't perfect, but it's a good indication that the risk is lower. The only other suggestion would be to see if there's another drug that will work to treat your condition that is a Category A drug. There are not very many Category A drugs, so you might not have a lot of success there. But it can't hurt to ask.
Apparently the FDA site is not very user friendly on this issue. Here's some text from a federal regulation on the subject that describes the drugs in that category (from the 2nd page of the PDF)
http://www.gpo.gov/fdsys/pkg/FR-2008-05-29/pdf/E8-11806.pdfPregnancy Category B
For pregnancy category B, if animal
reproduction studies have failed to
demonstrate a risk to the fetus and there
are no adequate and well-controlled
studies in pregnant women, the labeling
must state:
Pregnancy Category B. Reproduction
studies have been performed in (kind(s) of
animal(s)) at doses up to (x) times the human
dose and have revealed no evidence of
impaired fertility or harm to the fetus due to
(name of drug). There are, however, no
adequate and well-controlled studies in
pregnant women. Because animal
reproduction studies are not always
predictive of human response, this drug
should be used in pregnancy only if clearly
needed.
If animal reproduction studies have
shown an adverse effect (other than
decrease in fertility), but adequate and
well-controlled studies in pregnant
women have failed to demonstrate a risk
to the fetus during the first trimester of
pregnancy (and there is no evidence of
a risk in later trimesters), the labeling
must state:
Pregnancy Category B. Reproduction
studies in (kind(s) of animal(s)) have shown
(describe findings) at (x) times the human
dose. Studies in pregnant women, however,
have not shown that (name of drug) increases
the risk of abnormalities when administered
during the first (second, third, or all)
trimester(s) of pregnancy. Despite the animal
findings, it would appear that the possibility
of fetal harm is remote, if the drug is used
during pregnancy. Nevertheless, because the
studies in humans cannot rule out the
possibility of harm, (name of drug) should be
used during pregnancy only if clearly
needed.