I'm worried that your aquarium has not established a nitrogen cycle. If your aquarium is new that takes 4-6 weeks. If we keep adding fish, they keep adding the very toxic ammonia via their wastes. It takes time for an aquarium to grow a batch of beneficial bacteria which eat the ammonia and break it down into the somewhat less toxic nitrites. There will be a nitrite spike (too many PPM) and then a second batch of beneficial bacteria will break the nitrites down into the merely toxic nitrates.

We don't know much about your aquarium and so answers are a little generic. You don't have to answer all of them, but check the 40 items at
http://www.guppylog.com/story/2005/6/24/82111/0134

Those chemical spikes still need to be limited by use of weekly partial water changes of 25-45%. A second partial water change may be needed. The water should first be treated for whatever local water departments are putting in it. If at all possible, the water should sit a couple of days, though that is sometimes a luxury. At least the new water should be about the same temperature as that of the aquarium.

I often start a new 10-gallon/ 40-liter aquarium with only a pair of guppies or other small fish. If one can not "import" elements of a cycled aquarium (gravel, water, plants, even a filter) from an established tank, one must be very careful as the tank develops a nitrogen cycle.

Though it is an additional expense, buying test kits for ammonia, nitrites and nitrates are very useful. If the ammonia spike or a nitrite spike is going too high, there are several things which we can do.

The first is doing an additional partial water change. Collecting extra water bottles is not a bad thing so you are ready for that. :)

We can also put activated carbon in a filter. Especially in a new aquarium, it will probably not be chemically active for more than a week. There are other more expensive resins which can be used to pull extra ammonia out of an aquarium.

Plants can also be wonderfully useful and very attractive to the eye. But light, perhaps a watt per 2 liters or 2 watts/gallon for 13-16 hours day must be provided.

More careful feeding is beneficial too. Over feeding may kill more fish than any other single cause.

I'm not really familiar with them, but pet shops in some countries are now selling packages of beneficial bacteria with remarkable shelf lives. Adding them is also a wonderful way to "kickstart" the growth of beneficial bacteria.

For more more on the nitrogen cycle, we have a little on it in the second section of Immediate Help (link in the upper right hand corner of this page.) You might also use a search engine to look for Nitrogen Cycle. I would highly recommend The Everything Tropical Fish Book by Carlo Devito and Gregory Skokal, which is available in many American bookstores. There are a number of other good to excellent books aimed at newer aquarists.
 http://search.half.ebay.com/aquarium-fish_W0QQmZbooksQQpgZ19

Your name is really interesting, but makes me guess you may be from elsewhere than the US. Your libraries may have great aquarium books which will discuss the nitrogen cycle. Better shops, if you ask the experienced staff during "slow" hours, can be a great help, as can be local aquarium society members.

There have been a couple of times when I have directly contradicted guppylover427. I'm not trying to be mean, but adding fish at this juncture probably sentences them to death. The red in your female guppy's gravid area is probably a bacterial infection. Bacterial infections of that sort can usually not get by a fish's immune system  unless the water quality is less than it should be. Adding additional fish will just make the water worse.

Adding a treatment with an antibiotic may kill the fish anyway because it also kills the beneficial bacteria associated with the nitrogen cycle and then ammonia in the water skyrockets. Militant partial water changes of 25% the first day (with treated water of the same temperature, maybe seasoned a little) is the first step. You could pull the afflicted fish for a bath in a medication   treatment and return it to the tank. As many days as you can, walk up the partial water changes to 30%, 35%, 40%, 45% and on at 45%, 45%, 45%. That may clean up the water to the point where the guppy's immune system can reassert itself.

I'm sorry to sound so pessimistic. You may lose that female. With a lot of TLC (Tender Loving Care) you may help her back to health.

If you have the patience, just raise the fry. In the course of their growing up they will establish a nitrogen cycle and it will grow with them if you are faithful with partial water changes and feed them regularly but do not over feed them.