It could be pruritic and urticarial papules and plaques of pregnancy, otherwise known as PUPPPs.
Pruritic and urticarial papules and plaques of pregnancy (called PUPPP) is the most common skin disorder during pregnancy, occurring in 1 in 200 pregnant women. It is not known what causes PUPPP, but women who are pregnant with their first baby and have prominent stretch marks seem to be most affected. Itchiness is the major symptom along with small red bumps that usually first appear within stretch marks, with the area around the belly button being spared. The majority of PUPPP cases begin in the third trimester and resolve within a week of delivery. Treatment is supportive: oatmeal baths, emollient cream, cortisone cream, and antihistamines can all help.
The good news? PUPPPs tend not to recur. Also, some other skin disorders seen in pregnancy cause problems once a woman starts on hormonal birth control. Thankfully this tends not to be the case with PUPPPs.