Why do i have this bruise on top of my arm, it looks kind of brownish, i didnt fall on it or anything, its a little sore, why would i get that out of nowhere? saw my doctor 3 days ago but didnt have it then, did get bloodwork done,is it infected?

If that bruise is in the proximity of venipuncture site you probably have that because of the venous extravasation with blood work 3 days ago. If that is the case, color will be yellowish then disappear in the next 1-2 days.

Often people are unaware of trivial trauma that may cause bruising, especially in areas of thin skin or in people who take aspirin or meds like advil or Aleve or have deficiency of vit C,vit B12 or malnutrition. . It's not concerning unless you're experiencing diffuse easy bruising, frequent nose bleeds, gum bleeding or other bleeding events.