My DD, who is almost 5 months, has always had a good yell between 5pm and 6pm, when she gets her bedtime bottle. Today I had to let her cry a little, as I was getting dinner ready, but she was next to me in her bouncy chair. I was talking to her the whole time, but she wasn't too impressed with the potatoes and carrots I was peeling!
Normally what calms her down is a change of scene - I take her upstairs, and put her in her cot, which is in our bedroom - painted a very calming green. I wind up her mobile, and its like flicking a switch! Then I can get on with getting her bath ready.
I think she gets bored, together with getting tired and hungry. A good yell, followed by a good kick around tires her out nicely, and then she goes down really well at 7am ( or before
)
I think what is also important is not to get stressed yourself, especially if you know nothing is wrong - they really pick up on it if you are stressed, and this can make them cry more.
Hope this helps.