Quick tip on the excessive push / pull things: that's typically because you're being a tad too competitive with women, and they're responding in kind. Better way: if she starts acting competitive, don't compete. Just act bored: "Yeah, well..." look off to the side. Make her understand she's losing you by acting that way. If it's happening late in a seduction, it's moving backwards, which you need to discourage.
Knowing a girl likes you: I'm not entirely sure what that is, but I think girls are just checking you out / looking you up and down and you pick up on it subconsciously. The brain is amazingly sensitive to eye contact, even from a distance; you can stare into someone's eyes from across a huge, crowded room and they will immediately notice and lock eyes with you. I've had plenty of times I've stared at the back of people's heads and had them snap around and stare back (don't ask me how THAT one works). So most likely she's checking you out, tilting her body in your direction, playing with her hair, and your brain picks up on it and says, "That girl there. That girl likes you."
The girl you work with, sounds like she's trying to get you chasing her. She likes you, probably isn't 100% sure what she wants with you yet, but figures she'll give you proximity and see if you'll do anything with it. It'll stop after a while if you never do anything, and then she'll get cold and a little short with you, or just shift to neutral, depending on how much she likes you and how bad she's hoping you'll take action.