Is my rat pregnant yet or not?

i have a 10 month old female rat named Dawn, and we just recntly got a male named Sid. we wanted to breed them but i dont know how to tell if Dawn is pregnant yet or not. We keep them in seperate rooms all together, but we let them play on my bedroom floor, and sid chases her but i dont know if she got pregnant or not, and if she is shed only be like a couple days into it. And the 2 rats have been bickering a little...is that a sign?....please help!