Breastfeeding: Is this the end?

As a expectant mother, I had so many plans and ideas of how various things were going to be. Over the past 5 1/2 months, I have learned that some of these plans were ambitious, impossible and in some cases, foolish. I had not expected breastfeeding to fall into this category. Yet here I am. I had anticipated how I would go about weaning Taelyn. I had crazy ideas of the excitement I would feel when we hit this point. I had planned to wait until she turned one, or started biting me, which ever came first. Never would I have expected her to be done with me before I was ready to be done myself. Funny, everything else runs on her schedule, I just didn't expect this to follow suit.

Producing isn't the problem. I think it is more related to letdown. I don't feel super stressed, but for some reason, it is taking me longer than it used to. She is also giving me less time than she used to. After approximately 3 sucks, if she isn't instantly rewarded, she starts screaming (trust me, screaming is the right word). She is then too upset to continue trying. The more I try to force her to try again, the harder she screams. I feel frustrated, discouraged, and even...broken...
Feelings aside, this leaves me with one decision. Pump or use formula? I know which takes less time, but don't want to base my decision on which is easiest for me. Is breast milk really better than formula once we reach this point? Am I going to be hurting my baby by not feeding her breast milk? Hey Dad, maybe I'll pump and sell my milk to Ben & Jerry's!! Um...maybe not...

Any thoughts would be greatly appreciated. Let me clarify. Thought on pumping vs. formula at 5 1/2 months, not on Ben & Jerry's using breast milk instead of cows milk, would be best!