I second Epbrown's post. Also, do not quit breastfeeding, it will only add problems to your already extremely hectic life. Formula can't fix the problem either...if you think about it, breastmilk is the one thing that is designed exactly for your baby and her particular stage in life. Formula can't do that and is so much harder to digest, it may cause more problems than you already have.
One mother suggested nipple confusion...maybe you should read up about that and try to determine if your little one screams all of the time regardless of the fact that she nurses at the breast, or if she really is refusing to breastfeed and getting worked up about that to the point that she can't stop crying. If its not about the bottle, then it may be true colic and I'd ask your ped. about it at a visit, but be prepared for them to say that "that's just how some babies are at that age" as mine did until my baby screamed for 2 months and the ped. then said that "yeah, that sounds exactly like colic..."
The other mothers also had alot of good suggestions, but I would hesitate to say that colic doesn't exist and that it can be cured in a few simple steps. My youngest had colic from 6 or 7 weeks until the week he turned 4 mos. old. I don't want to kid you, it was very hard for our whole family, but it does end.. At one point, I thought that maybe I didn't even like my baby all that much, because I could see almost nothing of his actual personality, he just screamed and when he wasn't screaming, he was sleeping. Don't get me wrong, I totally love him, but it was hard when all I could see was him screaming, and rarely smiling or even looking content and happy.
Some babies have reflux, which causes pain and treating it can cure the colicky behavior. Ours did not, and was not even in actual pain all the time during his screaming. So if your little one is anything like that, maybe what we did will help you:
1. Check out askdrsears.com there is a section on dealing with fussy babies, and alot of the solutions help at least for a while.
2. I took caffeine out of my diet like you, which helped decrease some of the crying due to pain, as did eliminating onions, and deli turkey...don't know why the turkey, but maybe some sort of additive that they put in it when it's made into deli meat. My baby wasn't sensitive to spicy foods or dairy or anything else, just those 3 things.
3. My husband set his metronome (musician) on 60 beats per minute and turned it on when lo was particularly upset, and the repetitive beat seemed to calm him some. As did some music with a very distinctive drum beat...he actually liked the beach boys and Billy Joel.
4. We also had a little egg shaker/maraka (sp?) and a constant slow shake seemed to help calm him down a bit
5. I also prayed alot, and tried to remember that he was going to be fine and that he would come out this and that it does not last forever.
My little one is now 2 mos. free of colic and a happy little baby now. All of my family comments now how happy he is and how he doesn't scream all of the time now. YAY!
Anyway, if you ever need to talk...PM me.