I am experiencing a big spot on my thigh it is dark purple and red dots clumped up together no pain or anything i'm on depo what could this be?

Needs to be seen: It is impossible to say what something you are seeing on your skin is without being able to see it. New dark purple makes one think of bruise; however, there are other possibilities such as purpura and that can't be determined from your short question. I would advise you have either a virtual or in person appointment to address your concerns.