My 13 wk old DS has been fully BF since birth b...

My 13 wk old DS has been fully BF since birth but we have run into a hiccup. One side seems to be emptying REALLY quickly in the last couple of days, say 3 minutes compared to at least 10. I am offering this side first (is it a supply issue?) and within a couple of minutes, bub is getting frustrated at not getting enough. He then goes on the other side and will feed for at least 10 minutes. Could he and I be more efficent on the first side? I am still eating and drinking the same amount and tupes of food/water. He did have a couple of restless days earlier this week with not sleeping longer than half hour (thank goodness that has settled). In general DS is still the same happy boy he has been, even with the lack of sleep. I haven't experienced this before and wondered if anyone has??