H. - this exactly happened to me around the same age of my son, and this always happened in the late afternoon through the evening for us. I first want to say I am sorry you are going through this - I was so stressed because of it because I felt so bad that I didn't know what to do and didn't understand why my son was so mad.
I was given advice to go to kellymom.com. I read through many things and learned SO MUCH! It turns out that I realized he was so mad because my flow (let-down) was not fast enough. We were able to get a good flow the first couple minutes from me, but once it slowed down he had gotten very impatient which is why he screamed and arched his back. I tried what was suggested to try to speed up my flow, but sometimes it just didn't work for me. (If you have a slow flow, you are to massage, massage, massage, squeeze, squeeze, squeeze - there might be other tips on kellymom that I forgot about).
He nursed fine in the early am hours through noon (which would make sense because we all have more of a supply earlier in the day), but afternoons and evenings were a screamfest and nothing worked! After trying days and days, I started feeding him more often from a bottle; this calmed him down and he was so much more happy!
If you haven't checked out kellymom.com, you should. Look under the 2nd Column under Concerns - the first two bullet points could help.
http://www.kellymom.com/bf/index.html
Good luck! please keep us posted!!