Pregnacy

Despite how madly inlove I am with animals (and with my cat who I can brag about how affectionate and beautiful she is) this just shows how little I know about them!

My cat is breast feeding. It's been over three weeks already. She goes out not so often but my brother has seen her with the babies daddy a few times. She's also been eating allot to the point where she threw up once. If I don't put food out for her she eats the dogs food!!! She's eaten dog food before. She seems to like it. It's what she went for often when she was brought home and we had to kitty food for a while at first. I've been contoling her diet lately and not putting out dog food anymore lol they both get schedualed food now!
I've noticed a little belly in her. When she was pregnant the sides were filled out. She's got a little filled out right now, very little. But I wonder... can cats become pregnant more than once a year? And while breast feeding? How often are they supose to get their periods? I've heard dogs get it about twice a year and it lasts for about two weeks...

I can't have her pregnant again! I'm waiting for her kittens to grow and start eating caned and dry food so I can get her fixed finally. But I need to know if she's pregnant agian :/

?HELP?

PS: She loves the caned food, duh, so one for morning, one for lunch and one for dinner, and between those houres I put out about two spoon fulls of dry food for her to nibble on because I think she needs the energy to feed her babies. I could use some advise there too.