Breastfeeding help

First off I'm a first time mom and My son is 5 months old. For the past 2 months my breasts have felt like they did pre pregnancy. I know he's eating because he gulps during a feed. I'm just wondering is this normal or does this mean my supply is going down? I have to feed him off both breasts every hour and a half to 2 hours for a total of 10-15 minutes, but he's always been like that since he was around a month old.