hi bumblebee - it sounds like you are talking about my 5 week old daughter, alexa! she has grunted and strained since early days and i have laid awake for hours just praying she would stop, at the same time feeling realy sorry for her as it sounded unpleasant. however, she never cries so isnt distressed. i have spoken to my health visitor about it every time i saw her and she said it was normal. also discovered that so many babies do this - no consolation but i find it helps me to know i am not alone and that it will stop eventually.
alexa strains so noisilly before every poo - i think she just expresses herself really noisilly and i have to wait for her to grow out of it.
have a read of this Q&A in a US chat room about exactly the same problem.
http://www.babycenter.com/400_why-does-my-baby-seem-to-grunt-and-strain-all-day_2000690_164887873974.bc
i had advice from a friend today who said that her first baby grunted all night.....so she wore earplugs and said they really helped. she also had a fan on for white noise.
i am thinking of putting alexa in her own room (when its ready!) but i'm not ready yet - maybe in a month or two.interested in the mat that charliemum mentions.
I give alexa infacol before some of her feeds to keep the wind at bay as she suffered for a bit and also use a Dr Brown bottle for my expressed feeds as it is designed for colicky babies and means they take less air in. You can get them from boots, mothercare etc.
Take care and hope it improves for you quickly