Sun allergy during pregnancy?

Yesterday I started working in my garden for the first time this season and afterwards I noticed that I was getting an itchy, raised red rash on my chest. I was out in the sun again today (with sunscreen of course) and my chest rash looks a bit worse and now I have it on my forearm as well. The only thing I've done differently lately is being outside more, so I'm assuming it's some kind of heat rash or sensitivity to the sun? Has anyone else experienced this or have any idea what else it could be?