D.T.
Oh man... run, don't walk, to your doctor (best bet is a dermotologist) to get it checked out. It sounds like it could be PUPPPs - a specific 'pregnancy rash'. It may not spread, or it may spread to the rest of your body in a matter of hours. It doesn't look like a normal rash - more of a raised red spots. There are several 'pregnancy rashes' that look/act like it and most respond to typical over-the-counter solutions like topical cortizone creams. However, there is no cure for PUPPPs - it goes away after giving birth. The only approved treatment (since it's the only thing that seems to work) is a daily dose of predizone. It's totally safe for your baby - after all, it's what docs give mothers who are at risk for pre-mature birth to help speed up the baby's lungs development.
Many docs are clueless about PUPPPs, though. It is very often misdiagnosed - many women are told they have it when they don't. The only way to know for sure is to have a dermotologist do a biopsy(sp) and get you an answer in a day or two.