I nurse my son for 20 months. I remember hearing in breastfeeding class that it takes more work for a baby to get the breastmilk from your breast than it is to get formula (or breastmilk) out of a bottle. It could be as simple as your baby has figured that out and doesn't want to work that hard for breastmilk from your breast if he can get something (breastmilk or formula) from a bottle. The nurse who taught our class told us if we needed to use a bottle, to get the Nuk brand nipples. I guess if that is the case, get the slow flow type so your son can work harder for whatever is in the bottle. If you want to continue nursing, keep trying to breastfeed and keep pumping.
Another suggestion is a tough one: perhaps you could refrain from giving him a bottle when you're together so that he can remember how to nurse. I know the crying/screaming will probably get to you (my son's screaming still gets to me and he's 2), but if he's hungry enough, he'll try to nurse again if that's all you offer. If you're really worried about trying that method, you could always try feeding him breastmilk/formula with a spoon or through a tube. When my son was a newborn still in the hospital and my milk hadn't come in yet, we had to supplement with formula and did tube-feeding. The hospital had these little tubes that you could connect to a syringe. We filled the syringe with formula, my son would suck on my finger, and we slide the end of the tiny tube against my finger and into his mouth. Offer the breast first, then whatever other option you choose as a last resort.
Now, if he's crying hysterically WHILE you're trying to nurse...like, he latches on and starts to nurse but then stops, arches his back and cries, and your son might also spit up, have gassiness, and/or diarrhea, then the issue might be *your* diet and your son's sensitivity to something in it. I had to cut out a lot of foods while nursing because of my son's issues with my diet.
You might also want to contact the La Leche League. I'm sure they can give you some other tips on things to try if you really want to continue nursing.
If you have any other questions, please feel free to email me.