senigal chameleon

Question
why is there blood in my lizzards stool

Answer
First, the fact that you are asking this question here suggests you are not an advanced reptile keeper.  Senegal chameleons are an extraordinarily delicate species that no one who is not a highly experienced keeper should ever attempt.  Captive-bred specimens are almost impossible to find, and the vast majority of imports die very quickly.  They come in dehydrated, with massive parasite loads, injuries, and severe stress.  Only a small percentage will survive, with veterinary care and extreme diligence.

I say this to prepare you for the most likely outcome, not to be mean.  Your chameleon needs immediate veterinary attention and the equivalent of intensive care.  You must make sure that environmental conditions are nothing less than perfect--UVB, temperature, humidity, frequent showers, high air flow, and plenty of cover, in a quiet and solitary area of the home.  If you feel you have been misled as to the needs of this animal, you should immediately return it for a refund, and hopefully discourage the seller from repeating their actions of selling specialized, debilitated, delicate animals to the general public.

Here is a good starting point for you:  http://www.chameleonforums.com/

Ideal beginner lizards include leopard geckos, crested geckos, bearded dragons, and fat-tail geckos.  
Intermediate animals would include monitor lizards and basilisks (just examples).
All chameleons are advanced animals.  Among them, the hardiest are Veiled, Panther, and Jackson's chameleons, which are readily available as captive-bred, robust youngsters.  Senegal chameleons are among the least hardy...

Never buy a reptile from a pet store (other than a scant few select specialty stores).  Never take advice on reptile care from pet store personnel.  Always consult a veterinarian promptly for any medical issues.

The short answer is, the chameleon probably has blood in its stool because it has internal parasites.  These must be eliminated, or it will die.  There are other possible reasons, but that one is most likely.