I agree he is being overfed. You should talk to your DCPs about strategies to making the milk you pump last through the day. You can also try an even slower flow nipple, like the Breastflow. It really helped us when this was happening at about 5 months.
Another tip that I read was to make sure that the caregivers hold the baby often when not feeding, so that the LO doesn't associate being held with being fed every time. They may cry to be fed just for the attention if they aren't being held enough.Babies should be bottlefed:
For 10-20 minutes at a time, to mimic the usual breastfeeding experience. Care providers should be encouraged to make appropriate quantities last the average length of a feeding, rather than trying to feed as much as they can in as short a time as possible. This time element is significant because the infant's system needs time to recognize satiety, long before the stomach has a chance to get over-filled.
Consistent with a breastfed rhythm; the caregiver should encourage frequent pauses while the baby drinks from the bottle to mimic the breastfeeding mother's let-down patterns. This discourages the baby from guzzling the bottle and can mitigate nipple confusion or preference.
I would definitely try to find a way to get him off of the formula. If he's reacting to it, there may be a danger it could cause allergies or other problems for him long term. I know it is so difficult and confusing. I would encourage you to poke around www.kellymom.com. It saved my BF relationship with DD when we went through the exact same situation. Hang in there!!