Babies, OFTEN do what is called "cluster feeding." This means, that they NEED to, feed even every single hour. And this is NORMAL.
6 weeks is a growth-spurt time, in an infant. Every 3 weeks is a growth spurt. Then at 3 months, 6 months, 9 months and every 3 months.
At growth-spurt times, a baby gets hungrier and more often. Hence, feeding needs to be more frequent.
Feed on-demand, always. Per your baby's cues.
He is very young, their tummies are tiny. They feed until full. Then get hungry again. Normal.
Feeding a baby IS exhausting. Breastfed or Formula fed.
They feed all day and night. And need to. They are growing so fast and per development. Their intake needs, reflect that.
I nursed my son. But he would also take a bottle. I used the "MAM" brand bottle which I got from Amazon. It is also BPA free and has a natural nipple.
Nipple flow... will change as the infant gets older. The bigger nipple, for your son, is not working... he is choking. So don't use that.