So at least he is responding to your feeding routine.
Betta fish can actually be quite active and playful if you give him enough space with good water conditions. Usually in cooler than ideal water temperature, they would become inactive. In undersized tank without a lot of swimming space, they can also be inactive. If you give him a 5 gallon or even a 10 gallon, you'd see him swim around pretty much all the time.
How big is your pellet? If it is bigger than 1mm in size, then 1~3 should be enough for one feeding for a betta. If it is 0.5mm, then you might need 5~6+ for one feeding. My own personal routine is always one feeding a day which is the most common. There is nothing wrong with feeding every other day either, since quite some people do that too without any problem.
