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Well, you did the right thing when you were both sick, since that can make a baby more cranky and anxious that he does not have you around. , The crying it out method is alright to use. My only concern is that he is only 7 months old. At this age, he is still attached to you. You may want to continue to try this for another week or two and see if that helps him get used to it. It sounds like you are doing everything right, he just needs more time to adjust. :)
When my daughter was about 10 months I did try this and it worked after about one week.