Every so often I get what starts off as small red dots under the skin they then go darker and then the area turns yellow like a bruise no pain then go?

Unsure. These lesions need to be visualized & a history needs to be obtained in order to make an accurate diagnosis. Sometimes lab testing or biopsy is necessary. .
Difficult to tell. Skin issues are very difficult to diagnosis without actually seeing and touching the lesion. Occasionally, doctors may even need to biopsy or culture the lesion to make a determination. Best to see you family doctor or dermatologist to get you the best answer.