Bruise like rash on upper left thigh. was itchy then found a 5in by 5 covered with little bruises and large ones by it. is this serious?

Bruise: It is difficult to ascertain the nature of this rash just by description obviously, but it sounds to me as if you have what is called a "purpuric" rash along with scattered petechiae. There are many causes of this type of rash, but if they are occurring spontaneously then i would seek the care of a medical provider promptly for further evaluation.