Active While BFing

My LO is 12 weeks old and sometimes when he nurses he's super relaxed but other times hid arms are going nonstop. Especially his "top" arm. Even if he's partially asleep it will still flail around. I try to get him to hold onto a lovie, my shirt, my bra, but eventually I have to gently hold his arm to keep from getting whacked constantly. Is this normal and do you have any tips? I'm hoping he'll grow out of this or learn to hold on to something...