What Causes Arm Tiredness With Blood Vessel Prominence And Soreness?

Earlier today I was carrying the grocerys and noticed how tired I got in my left arm, but I didn't really give it much thought until I now saw that there seems to be a blood vessel that burst or something. It's a small blue/red spot and it's slightly turned outwards. It's a little bit sore, but not much. Have never seen anything like this before. I don't take any medications and I'm healthy. 22 years old. Anyone who knows what this might be, and if it's bad? Thanks!