It does sound worrying when baby doesn't like to feed as before.
I do agree with paed that most importantly, baby is gaining weight and is happy.
Perhaps he's very efficient at using whatever milk he drinks to grow?
Personally, I suggest avoiding force-feeding. This could create a negative emotion to feeding time and make things worse. I like to let baby associate feeding with happiness. I trust that when he's hungry, he'd ask for food and drink / eat fast. So far, it has been working.
During force-feeding, baby may swallow air and then throw up everything. No benefit to anyone.
Try alternative ways of feeding: use syringe, spoon or small cup. Maybe baby will be interested in the change? (Many mums have babies who rejected the bottle at some stage.)
Also, learn to relax. If you're frustrated, baby may be tense and less co-operative. (I learnt this the hard way with a fussy baby.) When you try and baby doesn't want to drink, let it go. Then try again 1/2-1 hour later.
Prepare small amount (about 2oz) when you try to feed. Then you'll have no stress that he has a lot to finish. And no stress of wastage. If he's happy to drink more, it's easy to prepare another 1-2oz.
As mums, we just got to keep trying and trying. All the best!