Terrible three’s?

I have a three year old who has started to really misbehave she is hitting and spitting and doesn’t listen when i put her in timeout all she does it get right back up. I praise good behavior with treats and sticker and things she likes. Timeout use to work but now it’s like she could care less what kind of punishment she gets. I don’t know if it’s because I’m pregnant and she won’t be getting all of the attention anymore but I’m extremely stressed out and feeling like I’m failing i need help.