M.,
What you are describing is something that many, many, many parents see. If you google 4 month sleep regression, you'll find a bit more info. Usually it happens around 19 weeks, and unfortunately, again, around 9 months. My dd went from 1-2 wake ups to waking almost every 1.5 hours. It was definately a rough patch for us.
as has been mentioned, there's a lot of stress on having our little ones sleep through the night, but the vast majority just dont' do it. I agree with you that crying it out is not a real solution. Dr. Jay Gordon has some great info on sleep out there, and even he advocates waiting until 1 year as the absolute minimum before trying to really sleep train your child.
Please, please take any info you get on starting solids with a grain of salt. Studies have disproven the "solids make them sleep through the night" theory. And yes, solids do keep them full "longer" because they're not capable of processing them at a young age. We held off starting solids until DD was 6.5 months old and her sleep was just as bad then. Developmental signs of readiness for solids include ALL of the following:
1. at least 6 months of age
2. able to sit unsupported
3. development of pincer grasp
4. loss of tongue thrust reflex
5. Active interest in eating, not just watching you or looking interested. You want them to be actively trying to grab food and cram it in their mouth.
You mentioned the Bjorn, have you looked at any other carriers? we have a great babywearing group in Wilmington that meets the 2nd thursday of the month. I found wearing DD helped me get her down for naps a lot easier.
We're still working out what works best for us at night. DD will be 18 months in a few days and we have good periods and bad nights. She sleeps in a crib in our room due to space issues in the house, but we hope to move in the not so distant future.
Hang in there mama, this too will pass. When we have a really bad night, I try to remind myself that in a year or four I'm going to have forgotten this and be missing my tiny little one.
S.