How do you tell weather you have acne or eczema?

This is a very humiliating topic for me to talk about, so bear with me please. I have bumps on my back and arms (Not like obsessively just like a patch here and there on my back and the bumps on my arm is a little more than on my back but it's stretched out more.) How do I tell the difference between acne and eczema? I need to know so I can treat it properly. Thank you all so much!