Besha'ah tovah!
Bleeding
attributable to a vulvar abscess such as you describe does not make you
niddah. Especially if your physician can confirm your evaluation, no further halachic steps are necessary.
A
pregnant woman can become
niddah from uterine bleeding, with the usual procedure for
becoming tehorah.
Staining is fairly common during pregnancy. For that reason, pregnant women should continue to take
niddah-related precautions such as wearing colored underwear, having relations on colored sheets, etc.
We wish you a refuah sheleimah!