I'm sorry for your trouble! I have had mastitis too and I know it hurts so bad! But feeding your baby more bottles will not make you feel any better, he NEEDS to nurse the pain away for you! Your breast pump does not have the same suction or the same effectivness at nursing that your baby does, nursing is really the BEST way to get rid of the plugged duct and the pain. And don't worry, the milk is still clean, the infection from mastitis does not acctually reside in the milk.
If he is having trouble getting started nursing you can use a trick I learned from a lactation consultant; have a small cup of expressed milk and a medicine syringe ready, you can buy a medicine syringe or just use one that came with some kid's Tylonel or whatever, it needs to be the depressor kind though, the kind that is like an eye droppper doesn't work as well. Suck some expressed milk up with a medicine syringe, when your son latches on and begins to suck, sneak the syringe in the corner of his mouth and squirt some milk into his mouth. It helps if you can get your husband or another helper to do that for you. Then he will keep nursing because he is getting some milk! After a little while when your milk begins to flow stop using the syringe.
Another idea is to lie down in bed with him when you nurse, you will be more relaxed and he will feel more relaxed too. He may be getting upset when you try to nurse him becasue he can feel your tension, which is understandable since you feel so cruddy!
Nurse your baby as frequently as you possibly can, and always start with the side with the plugged duct. DON'T give him ANY bottles because then he will not want to nurse and you'll still have that plugged duct. When you are feeling better he can have bottles while you're at work again, but when he si home with you just nurse him, it's healthier for you both. You are doing such a great job nursing your baby, don't give up because it is worth it! Best of luck to you!