skin rash

Okay here's the thing I'm 27 weeks with my second child (first is 9 1/2 months) and for the past couple weeks I have been getting a recurring rash. When I first got it it was only on my forearms then the next day it was my arms and breasts. It went away for about a week and last night it showed up on my arms breasts and stomach. It shows up in the evening between 6 and 8 and goes away in a few hours. It basically looks like a bunch of mosquito bites when it first appears and as it goes on the bumps grow together to make 1 large red itchy bump. I haven't been in contact with anything new or ate any new foods. I have a dr appt tomorrow and I plan on asking her about it but I'm nervous because so far all she's done is prescribe me drugs for every small problem I have. Does anyone know what this could be? Any ideas for making it go away? Anything would help this rash is driving me crazy!