I can't feel my arms!

Did my firsty proper circuit today, thought it was gonna be a bit easy but boy was I wrong. You go through about 20 stations in the circuit, and you go around twice, changing stations every 30 seconds or so. You alternate between a cardio station and a weights station. Now I could do cardio for hours, but I've never done weights properly before. My arms are a bit like jelly at the moment .. it's great! Bring on the muscles lol.