How can I tell if a cat is pregnant? Why won't he/she eat?

Some piece of scum left this cat in a carrier at the entrance of my neighborhood, obviously hoping someone would take it. I am an animal lover so of course I did, I mean it was like 100 degrees outside! And there was no water or food or anything, just a cat in a dusty, dirty, old carrier. The cat isn't dirty though at all in fact its very sweet and soft and cute. Doesn't look over 2 years old. However I can't get it to eat. I'm trying to feed it a can of Friskies and it kind of licks at it when I start hand feeding it but it acts like its afraid to actually chew it, even when I put it on the ground it wont eat it, it will only lick it. Also it hasnt drank any water and its been like 12 hours almost. I cant tell if its a boy or girl so how can I tell? Also its really fat, and i think, if its a girl, it looks pregnant. the fat isnt so much flubbery but more hard. i googled earlier how to tell if a cat is pregnant and it mostly said to check its nipples but the cat is so nervous i cant get it to sit still for me to look at them. i tried feeling for them and i dont feel anything. what do i do? it doesnt seem sick but should i got to the vet? or is it normal for a cat not to want to eat or drink when in a new environment? i really just want whats best, thank you for helping!