Uneven milk production

Hi all. My son is 6 weeks old and is breastfed, besides 200ml of formula a day (so I can have a lay in and go to bed early). I also pump once or twice a day depending on his naps. I offer both sides per feed and 90% of the time he spends roughly the same amount of time on each boob. I’ve noticed however when pumping (in the last 2 weeks or so) that my left side produces nowhere near the same amount as my right. For example, I pumped earlier today, for 15 mins, an hour after my son had fed on both sides. My right side produced 100ml but my left barely 20ml - both boobs felt full! I’m not concerned about his weight gain as he surpassed his birth weight within 1 week and has plenty of wet and dirty nappies. I just wanted to know if anyone else has this?