new to breeding rats

Just 2 questions. Can you rebreed a female before you remove her pups, they are 3.5 wks old or How soon after you remove pups can you breed her again. I need pups . but only 1 of my female rats is producing , I only have 3 females .

Can you rebreed her? Yes. Some people do harem style breeding and have a good amount of success from it. Harem breeding is leaving a male in with a group of females throughout their cycle. He'll usually breed the female within a few hours of giving birth.

Now, would I suggest it? No, not really. I believe the females need a small break. By doing this, I usually have a pretty high litter count (I haven't had less than 13 pups in a few years). Usually having more like 15-18 pups per litter. Your female is also likely to be able to produce longer, but overall won't have as many pups as if you had done a harem breeding.

Since it's been 3.5 weeks since her last breeding, you aren't really doing a harem breeding as much as a back to back. While I'd wait a few weeks (at least) after she has them weaned to breed her again, you can have her bred right now. It's all up to you and what your longterm goals are and how you feel about the animals. Everyone has their own style of breeding rodents and it all works.

Tl;dr: It's healthier for the female if you wait until the pups are weaned and you've given her a few weeks off before breeding her again. That being said, she will breed right now if you want.

It depends on how you breed, like mentioned above..
I personally do harem breeding, with no breaks, 1.3 in a tub. My females start breeding at 4 months, and I retire them at 12 months.
I used to pull preggos, and put in individual tubs, but I find that harem is still the best way to do it.
I built a 72 slot condo for preggos, it wasn't cheap either... I've since refurbished it and gone back to harem breeding....
My females have 10-14 averages... I pull any that don't produce better than that after two litters.

I breed 1 female to 1 male at a time and want to try to keep pups around at least for the next year. I have 3 females and 2 males all in seperate cages. Only 1 of my females is giving pups so far , her first litter 3.5 weeka ago was only 4 pups. I've tried my females with each male and only had this 1 litter. Any help anyone can give me will be taken and tried. I'm breeding for my snakes , pet store rats here are 9.00 for fuzzies and 10.95 for small , live or frozen , so I'm trying to save a little money.

Drop one male in with the 3 females, and let them go at it....
All there is to rats.

Look on craigslist or post a wanted add for people who breed rats in your area. Get a few high quality females and raise them up. Hold back all females from the lines you want to continue to breed.

Along with their diet (I would suggest rodent block, but many have success with Doggy Bag dog food and a few other brands), feed table scraps (grains, chicken bones, cereals, veggie noodles, fruits, veggies, etc). This will help them keep a healthy weight as well as help them lactate when they have their pups.

Make sure they are not kept somewhere too warm or cold, this will slow production. The rats will be more focused on maintain their body temperature than reproducing.

Also, it could be that you have a lazy male, which is another reason to find a rat breeder in your area. I would pick up two-three males and at least six females. Hold back the male that breeds the best for you, and the females that produce the most and care for the pups the best. Usually after finding a group that breeds well, you can then focus on traits such as color and personality. Never hold back a female that eats her young, even on her first litter. I've never had a female who devoured her young not turn around and do it again.