So I got 2 rats a little over 2 weeks ago. I am almost positive that one of the 2 is pregnant. She just eats sleeps and drinks. Her nipples are clearly shown. She is quite aggressive toward her cagemate (sister) and not me. She bit me once on the day after I got her. My only worry is that she goes into heat sometimes. Is she pregnant or not? Please help me ASAP!
P.s she is also chubby and when she lays down it looks like she swallowed 2 golf balls. Thanks.

Yes she might be. I had 3 rats once (2 females and 1 male). One of the females got pregnant and acted aggressive. In the middle of the night i heard unusual scurrying around the cage. There were like 20 lil pinkies in there and she was trying to clean them n chase the big rats away. I took the mom out and got her in her own cage with her babies. She bit me lke 3 times while i was trying to put her babies in the cage. She thought i was hurting them. I took her to the pet store because i didn't know what to do with the babies. They were cute though :)

It is hard to tell from the description because most of those things are fairly common. If she was housed with males, though, she probably is pregnant, most females housed with males will be, if they were, it is surprising that both of them aren't pregnant. If you are sure she is going into heat, then she cannot be pregnant, but how do you know she is in heat? Well the gestation period for rats is only about 23 days sometimes less, so if you got her over 2 weeks ago, she will have babies very soon if she is pregnant. pets question and answers,www.5d2d.com

If you suspect she's pregnant, you might want to separate her from her sister, especially if she is being aggressive. Give her plenty of food, water, and nesting materials and maybe some extra protein. If in another week or so she doesn't have babies then you can put her back with her sister.