You said he "seems to have reflux..."
So did you take him to the Doctor and remedy that?
Reflux makes babies unable to sleep and uncomfortable.
Are you feeding him on-demand?
If nursing, do you have enough milk? Is he latching on properly? If not... then a baby will always be hungry and not be satisfied nor able to sleep.
This sounds basic, but its what happened to lots of my friends. They didn't have enough milk and their baby was hungry. They didn't know. And the baby was not latching on properly... thus the baby was not satiated.
He is so young... they usually nap a lot.
Maybe he is sensitive to noises/temperatures/lighting/etc.
My daughter as an infant, would wake even if the toilet flushed anytime. She has real sensitive ears.
Does he have gas problems? This is another reason why some babies are uncomfortable.
Burp him frequently or give him infant gas drops. It helped my daughter a lot.
In infants, growth-spurts also occurs every 3 weeks... then at 3 months, 6 months, 9 months and so forth every 3 months. They need extra intake at these times especially. And infants will frequently "cluster feed" meaning they need to feed even every hour.
Thus, feed on-demand.
Over-tired babies and children, also do not sleep better and sleep worse and have a harder time falling asleep and they wake more.
Do you know his 'tired' cues???
An infant, will typically get tired after about 2 hours of "awake" time. And if over-stimulated, they can have a hard time sleeping and settling down as well.
all the best,