you must be exhausted! Your first stop should be to the pediatrician, because you want to rule out anything medical. Conditions like reflux, milk allergies, or apnea could all be waking her up. You can help your physician by recording her frequency and behaviors around waking (is she arching, turning red, giving a 'pain cry'?). Let the pediatrician know about any dietary changes you have made (new brand of formula etc). Some babies are sensitive to laundry detergents, so make sure you are using a detergent made for infant clothes. Some are also sensitive to perfumes, so check around and see if a new air freshener or fabric softener could be causing her discomfort. Hopefully you will hear that its just gas or colic, as most of the time its anyone's guess as to why a little one is having a hard time sleeping.
In terms of responding to her, I personally believe that we should respond when a young baby cries within a few minutes. If she is the type who can settle back down after couple of minutes, then let her do so, but if she is the type where she just gets more agitated, then letting her 'cry it out' can be awful for everyone involved. You can help her learn to soothe herself little by little. Instead of taking her out of the crib every time, try giving a paci, putting a hand on her belly or speaking softly. If you are breastfeeding, it might be better for your husband to do this, so that she won't expect a feeding or to use you as a human pacifier. See how often you can get away with soothing her without actually taking her out of the crib, and try to expand the length of this time little by little.
Most babies adjust to the sound level in their house, so I am guessing that noise is not the real trigger. You can get devices that make soothing sounds. The danger in getting a 'white noise' generator or music player is that they can become dependent on it. You can also get vibrating crib pads, but again, be prepared that she will come to expect it every time. However, it may be worth trying in your case.
Hmm an interesting dilemma, I would say it's too soon for sleeping pills haha. Your best bet is to stick with it, after a while she won't need the rocking anymore and she'll sleep for longer amounts of time, it just takes some getting used to.