my kitty.. few questions

ok im not sure what all those buttons are up there LOL figure those out later..i guess my message will be plain until then. My name is Corina and i have 2 cats, one i got as a little kitten, im not sure what kind she is.. she has very dark colors and shes really fluffy and has no tail, and shes terribly unsocial.. i gave up on her, i love her but let her be.. ive never been able to pick her up, i can pet her, but cant hold her, and she'll even sleep on my bed with me.. she sure loves me when i got food though.. shes finicky also..VERY.. only eats certain food and wont ever touch people food, not even a fish stick LOL ive had her for 3 years now, the problem is my other cat, i got her from my sister who couldn't take care of her anymore, she was a kitten and we had future plans to spay her, shes a house cat we figured no rush really, we figured closer to spring. anyhow she went into her first heat last month, made me wish i had spayed her sooner, she never would go outside, she hated it and acted scared, so we never had to worry about her accidentally running out..well when she was in heat she got out ONE night, we still don't know how, i guess cats in that condition find away..then i was thinking we live so far out their wont be any males around.. WRONG!! their smell is pretty powerful, anyways she came home with this other cat, im assuming it was a male, she came in and never been out since! So im not sure if she's pregnant that was like 5-6 weeks ago.. please no hateful remarks, i feel bad enough about it, and im getting her fixed in march .. thats if shes not pregnant, the thing is her behavior has been strange, she has always gotten along with the other cat, they've been like best friends, they constantly played and cleaned each other, now she wont have anything to do with her, and if she comes near her she hisses at her, they are definitely not friends anymore, she also eats more and sleeps more. I'm just wondering if pregnancy causes a cats behavior to change in that way, (I know when i was pregnant i hissed at people too LOL) where they no longer want to socialize with other animals.. this has been such a friendly cat, and shes beautiful..she has a green eye and a blue eye, and shes solid white! i have two guinea pigs also, and she even got along with them.. its so cute.. she use to play with the piggys. I'm just not sure what to make of this behavior, wondering if she just matured some, or its hormones. Thanks!

Usually pregnancy doesn't effect thier attitude twards cats they are friends with. If you think it's been about 5-6 weeks, you would be able to tell by her size and if her nipples are pink and enlarged. Cats only have a gestation period of around 63 days.
With the change in attitude, my guess is that she is just hormonal. Unspayed females are much more territorial and not as friendly. If she IS pregnant, I suggest you put her in a room of her own until the kittens are weaned and she is spayed. Then you can gradually re introduce the 2 of them.