How old is he?
Did you ever see a Lactation Consultant? If not, do so.
Some babies, once they drink from a bottle, will then only want a bottle. Why? Because, a bottle is much easier to drink from.. the baby does not have to 'work' at it. A bottle is just by gravity. Versus, with a breast, a baby has to work at it harder, in order to get the let-down started and then to suck to nurse. For breastfeeding, it takes mouth/tongue coordination... and for some, the letdown can be slow, hence a baby gets impatient. Or the flow of milk, is slow or not enough. Or the supply of milk is not enough.
Nurse him... with both boobs, per session. Until you are empty. THEN, give him a bottle as a 'chaser.'
Otherwise, your milk supply, will decrease.
Nursing him for only a couple of minutes, might not be long enough... for him to get to the hind-milk and to keep your breasts productive enough.
Pumping, does not stimulate the nipples as much. Depending.
Do you have, ample milk or not?
If not, then maybe your baby is refusing the breast, because of that too.
You need to see a Lactation Consultant.
Is he teething?
When babies teethe, they often 'reject' breast, because their gums hurt.
But it passes.
How come you are getting sores on your breasts?
To me, this indicates, that he is NOT latching on, properly.
The ENTIRE areola, should be in the baby's mouth. Not just on the tip of the nipple. AND you should see and hear, the baby sucking and swallowing.
Who, 'diagnosed' him with low blood sugar? And that thus, he exerts too much energy, while nursing? I had never heard of that. Did the Pediatrician actually say this and to bottle feed him?